Moved plugins and refactor command system

- Moved plugins to apropriate sub folders
- Refactor command system with new add_command method and rename GetCommandSystemEvent to GetNewCommandSystemEvent
- Add RegisterCommandEvent for dynamic command registration
- Change footer container orientation to VERTICAL
- Add search-highlight tag to source buffer
- Add file change detection (deleted, externally modified) in source_file
- Add JSON prettify option to source view popup menu
- Enable hexpand on VTE widget
- Update plugins_controller_mixin to use widget_registry

src/core/widgets/vte_widget.py

@@ -45,6 +45,7 @@ class VteWidget(Vte.Terminal):
         ctx.add_class("vte-widget")
 
         self.set_clear_background(False)
+        self.set_hexpand(True)
         self.set_enable_sixel(True)
         self.set_cursor_shape( Vte.CursorShape.IBEAM )