Moved mirage2 to use newer GTK template structure patterns

src/plugins/plugins_controller_mixin.py

@@ -0,0 +1,20 @@
+# Python imports
+
+# Lib imports
+
+# Application imports
+
+
+
+class InvalidPluginException(Exception):
+    ...
+
+
+
+class PluginsControllerMixin:
+
+    def request_ui_element(self, target_id: str):
+        if not target_id in widget_registery.objects:
+            raise InvalidPluginException('Unknown UI "target_id" given in requests.')
+
+        return widget_registery.objects[target_id]