Clean up deprecated code and fix multiple issues

- Remove deprecated markdown_preview plugin and re-wrote
- Renamed alt_provider.py under words completer
- Fix words completion provider logic and cache handling
- Fix container orientations (VERTICAL -> HORIZONTAL) and add Separators
- Remove unused Gtk imports from search_replace plugin
- Fix event creation parameter order in source_file.py
- Fix typo in source_view.py (_load_pretify_json -> _load_prettify_json)
- Refactor webkit_ui with new load methods and enhanced settings

plugins/code/markdown_preview/markdown_preview.py

@@ -0,0 +1,101 @@
+# 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 core.widgets.webkit.webkit_ui import WebkitUI
+
+from .mixins.markdown_preview_mixin import MarkdownPreviewMixin
+
+
+
+class MarkdownPreview(Gtk.Popover, MarkdownPreviewMixin):
+    def __init__(self):
+        super(MarkdownPreview, self).__init__()
+
+        self.can_hide: bool          = True
+        self.is_preview_paused: bool = True # True by default b/c started hidden
+
+        self._setup_styling()
+        self._setup_signals()
+        self._load_widgets()
+
+
+    def _setup_styling(self):
+        ctx = self.get_style_context()
+        ctx.add_class("markdown-preview")
+
+        self.set_modal(False)
+        self.set_can_focus(False)
+        self.set_transitions_enabled(False)
+        self.set_size_request(480, 720)
+        self.override_background_color(
+            Gtk.StateFlags.NORMAL,
+            Gdk.RGBA(0, 0, 0, 0.0)
+        )
+        self.set_constrain_to(
+            Gtk.PopoverConstraint.WINDOW
+        )
+
+    def _setup_signals(self):
+        self.connect("hide", self._handle_hide)
+        self.connect("show", self._handle_show)
+
+    def _load_widgets(self):
+        box             = Gtk.Box()
+        bttn_box        = Gtk.ButtonBox()
+        scrolled_win    = Gtk.ScrolledWindow()
+        viewport        = Gtk.Viewport()
+        self._markdown_view       = WebkitUI()
+
+        self.start_stop_bttn = Gtk.ToggleButton()
+        settings_bttn   = Gtk.Button()
+
+        self.start_stop_bttn.set_label("gtk-media-pause")
+        self.start_stop_bttn.set_use_stock(True)
+
+        settings_bttn.set_image(
+            Gtk.Image.new_from_stock(
+                "gtk-justify-fill",  Gtk.IconSize.BUTTON
+            )
+        )
+
+        self._markdown_view.set_vexpand(True)
+        box.set_orientation(Gtk.Orientation.VERTICAL)
+
+        self.start_stop_bttn.connect("clicked", self._tggle_preview_updates)
+        settings_bttn.connect("clicked", self._handle_settings)
+
+        bttn_box.pack_end(self.start_stop_bttn, expand = False, fill = False, padding = 1)
+        bttn_box.pack_end(settings_bttn, expand = False, fill = False, padding = 1)
+        viewport.add(self._markdown_view)
+        scrolled_win.add(viewport)
+        box.add(bttn_box)
+        box.add(scrolled_win)
+        self.add(box)
+
+        box.show_all()
+
+
+    def _handle_hide(self, widget):
+        if self.can_hide:
+            self.is_preview_paused = True
+            return False
+
+        return True
+
+    def _handle_show(self, widget):
+        self.can_hide = False
+        self.is_preview_paused = self.start_stop_bttn.get_active()
+
+    def _tggle_preview_updates(self, widget):
+        self.is_preview_paused = not self.is_preview_paused
+
+    def _handle_settings(self, widget):
+        ...