Refactor controller architecture and multi-insert state

- Rename ControllerContext to ControllerMessageBus for clarity
- Switch ControllerBase to use SingletonRaised
- Replace MarkEventsMixin with MarkerManager for multi-cursor editing
- Add populate_popup event support for source view context menus
- Remove unused swap file events
- Moved JSON prettify feature to plugin
- Fix event name: "removed_file" -> "remove_file"

src/libs/controllers/emit_dispatcher.py

@@ -8,6 +8,13 @@ from ..dto.base_event import BaseEvent
 
 
 class EmitDispatcher:
+    """
+        EmitDispatcher is used for allowing controllers to pass/hook in
+        their message system to children that need to signal events.
+        Note how we are not handling return info from the 'message' methods
+        whereas a controller would or could do so.
+    """
+
     def __init__(self):
         super(EmitDispatcher, self).__init__()