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

plugins/code/completers/snippets_completer/plugin.py

@@ -0,0 +1,39 @@
+# Python imports
+
+# 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
+
+from .provider import Provider
+
+
+
+class Plugin(PluginCode):
+    def __init__(self):
+        super(Plugin, self).__init__()
+
+        self.provider: Provider = None
+
+
+    def _controller_message(self, event: Code_Event_Types.CodeEvent):
+        ...
+
+    def load(self):
+        self.provider = Provider()
+
+        event = Event_Factory.create_event(
+            "register_provider",
+            provider_name = "Snippets Completer",
+            provider      = self.provider,
+            language_ids  = []
+        )
+        self.message_to("completion", event)
+
+    def run(self):
+        ...