Refactor controller architecture and multi-insert state

- Rename ControllerContext to ControllerMessageBus for clarity
- Switch ControllerBase to use SingletonRaised
- Replace MarkEventsMixin with MarkerManager for multi-cursor editing
- Add populate_popup event support for source view context menus
- Remove unused swap file events
- Moved JSON prettify feature to plugin
- Fix event name: "removed_file" -> "remove_file"

plugins/code/prettify_json/plugin.py

@@ -0,0 +1,55 @@
+# Python imports
+import json
+
+# Lib imports
+import gi
+
+gi.require_version('Gtk', '3.0')
+
+from gi.repository import Gtk
+
+# Application imports
+from libs.event_factory import Event_Factory, Code_Event_Types
+
+from plugins.plugin_types import PluginCode
+
+
+
+def _load_prettify_json(buffer, menu):
+    menu.append( Gtk.SeparatorMenuItem() )
+
+    def on_prettify_json(menuitem, buffer):
+        start_itr, \
+        end_itr = buffer.get_start_iter(), buffer.get_end_iter()
+        data    = buffer.get_text(start_itr, end_itr, False)
+        text    = json.dumps(json.loads(data), separators = (',', ':'), indent = 4)
+
+        buffer.begin_user_action()
+        buffer.delete(start_itr, end_itr)
+        buffer.insert(start_itr, text)
+        buffer.end_user_action()
+
+    item = Gtk.MenuItem(label = "Prettify JSON")
+    item.connect("activate", on_prettify_json, buffer)
+    menu.append(item)
+
+
+
+class Plugin(PluginCode):
+    def __init__(self):
+        super(Plugin, self).__init__()
+
+
+    def _controller_message(self, event: Code_Event_Types.CodeEvent):
+        if isinstance(event, Code_Event_Types.PopulateSourceViewPopupEvent):
+            language = event.buffer.get_language()
+            if not language: return
+
+            if language.get_id() == "json":
+                _load_prettify_json(event.buffer, event.menu)
+
+    def load(self):
+        ...
+
+    def run(self):
+        ...