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/containers/footer_container.py

@@ -26,7 +26,7 @@ class FooterContainer(Gtk.Box):
         self.ctx = self.get_style_context()
         self.ctx.add_class("footer-container")
 
-        self.set_orientation(Gtk.Orientation.HORIZONTAL)
+        self.set_orientation(Gtk.Orientation.VERTICAL)
         self.set_hexpand(True)
 
     def _setup_signals(self):