Remove tabs UI from code editor and move to plugin. Enhance plugin system.

- Remove tabs controller, tab widget, and tabs widget files and move to plugin
- Delete plugins/README.txt
- Add register_controller method to controller system for plugin use
- Add error handling for plugin crashes via futures callback

plugins/code/tabs_bar/tabs_widget.py

@@ -0,0 +1,179 @@
+# Python imports
+
+# Lib imports
+import gi
+gi.require_version('Gtk', '3.0')
+gi.require_version('Gdk', '3.0')
+from gi.repository import Gtk
+from gi.repository import Gdk
+
+# Application imports
+from libs.event_factory import Event_Factory, Code_Event_Types
+
+from .tab_widget import TabWidget
+
+
+
+class TabsWidget(Gtk.Notebook):
+    def __init__(self):
+        super(TabsWidget, self).__init__()
+
+        self._setup_styling()
+        self._setup_signals()
+        self._subscribe_to_events()
+        self._load_widgets()
+
+        self.show()
+
+
+    def _setup_styling(self):
+        self.set_scrollable(True)
+
+    def _setup_signals(self):
+        self.connect("page-added", self._page_added)
+        self.switch_page_id = \
+            self.connect_after("switch-page", self._switch_page)
+
+    def _subscribe_to_events(self):
+        ...
+
+    def _load_widgets(self):
+        ...
+
+    def _page_added(self, notebook, page_widget, page_num):
+        tab = self.get_tab_label(page_widget)
+        tab.set_close_signal(self._close_tab)
+
+        self._bind_tab_menu(tab, page_widget)
+
+        page_widget.show()
+        self.set_tab_detachable(page_widget, True)
+        self.set_tab_reorderable(page_widget, True)
+
+    def _close_tab(self, button, file):
+        event = Event_Factory.create_event(
+            "remove_file",
+            buffer = file.buffer
+        )
+
+        self.message(event)
+
+    def _switch_page(self, notebook, page_widget, page_num):
+        tab   = self.get_tab_label(page_widget)
+        event = Event_Factory.create_event(
+            "set_active_file",
+            buffer = tab.file.buffer
+        )
+
+        self.message(event)
+
+    def _bind_tab_menu(self, tab, page_widget):
+        def do_context_menu(tab, eve, page_widget):
+            if eve.type == Gdk.EventType.BUTTON_RELEASE and eve.button == 3: # r-click
+                menu = self.create_menu(page_widget)
+                menu.popup_at_pointer(eve)
+
+        tab._eve_handler_id = \
+            tab.event_box.connect(
+                "button-release-event",
+                do_context_menu,
+                page_widget
+            )
+
+    def create_menu(self, page_widget) -> Gtk.Menu:
+        context_menu     = Gtk.Menu()
+
+        close_item       = Gtk.MenuItem(label = "Close Tab")
+        close_left_item  = Gtk.MenuItem(label = "Close Tabs Left")
+        close_right_item = Gtk.MenuItem(label = "Close Tabs Right")
+        close_other_item = Gtk.MenuItem(label = "Close Other Tabs")
+        close_all_item   = Gtk.MenuItem(label = "Close All Tabs")
+
+        close_item.connect("activate", self.close_item, page_widget)
+        close_left_item.connect("activate", self.close_left_items, page_widget)
+        close_right_item.connect("activate", self.close_right_items, page_widget)
+        close_other_item.connect("activate", self.close_other_items, page_widget)
+        close_all_item.connect("activate", self.close_all_items, page_widget)
+
+        context_menu.append(close_item)
+        context_menu.append(close_left_item)
+        context_menu.append(close_right_item)
+        context_menu.append(close_other_item)
+        context_menu.append(close_all_item)
+
+        context_menu.show_all()
+
+        return context_menu
+
+    def view_changed(self, buffer):
+        for page_widget in self.get_children():
+            tab = self.get_tab_label(page_widget)
+            if not buffer == tab.file.buffer: continue
+
+            self.handler_block(self.switch_page_id)
+
+            self.set_current_page(
+                self.page_num(page_widget)
+            )
+
+            self.handler_unblock(self.switch_page_id)
+
+            break
+
+    def modified_changed(self, buffer):
+        for page_widget in self.get_children():
+            tab = self.get_tab_label(page_widget)
+            if not buffer == tab.file.buffer: continue
+
+            ctx = tab.label.get_style_context()
+            ctx.remove_class("file-deleted")
+            if buffer.get_modified():
+                ctx.add_class("file-changed")
+            else:
+                ctx.remove_class("file-changed")
+
+            break
+
+    def externally_deleted(self, buffer):
+        for page_widget in self.get_children():
+            tab = self.get_tab_label(page_widget)
+            if not buffer == tab.file.buffer: continue
+            ctx = tab.label.get_style_context()
+            ctx.add_class("file-deleted")
+            break
+
+
+    def close_item(self, menu_item, page_widget):
+        tab = self.get_tab_label(page_widget)
+        tab.close_bttn.clicked()
+
+    def close_left_items(self, menu_item, page_widget):
+        children = self.get_children()
+        i        = children.index(page_widget)
+
+        if i == 0: return
+
+        for widget in children[ : i]:
+            tab = self.get_tab_label(widget)
+            tab.close_bttn.clicked()
+
+    def close_right_items(self, menu_item, page_widget):
+        children = self.get_children()
+        i        = children.index(page_widget) + 1
+
+        if i == len(children): return
+
+        for widget in children[i : ]:
+            tab = self.get_tab_label(widget)
+            tab.close_bttn.clicked()
+
+    def close_other_items(self, menu_item, page_widget):
+        self.close_left_items(menu_item, page_widget)
+        self.close_right_items(menu_item, page_widget)
+
+    def close_all_items(self, menu_item, page_widget):
+        children = self.get_children()
+
+        for widget in children[ : ]:
+            tab = self.get_tab_label(widget)
+            tab.close_bttn.clicked()