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"

plugins/code/prettify_json/manifest.json

@@ -0,0 +1,7 @@
+{
+    "name": "Prettify JSON",
+    "author": "ITDominator",
+    "version": "0.0.1",
+    "support": "",
+    "requests": {}
+}