Moved plugins and add loaded file filtering

- Moved prettify_json and lsp_completer plugins to sub categories
- Add filter_out_loaded_files to prevent opening already-loaded files
- Refactor code events into single events module
- Fix signal blocking during file load operations
- Include READONLY state in source view lifecycle handling

plugins/code/event-watchers/prettify_json/prettify_json.py

@@ -0,0 +1,31 @@
+# Python imports
+import json
+
+# Lib imports
+import gi
+
+gi.require_version('Gtk', '3.0')
+
+from gi.repository import Gtk
+
+# Application imports
+
+
+
+def add_prettify_json(buffer, menu):
+    menu.append( Gtk.SeparatorMenuItem() )
+
+    def on_prettify_json(menuitem, buffer):
+        start_itr, \
+        end_itr = buffer.get_start_iter(), buffer.get_end_iter()
+        data    = buffer.get_text(start_itr, end_itr, False)
+        text    = json.dumps(json.loads(data), separators = (',', ':'), indent = 4)
+
+        buffer.begin_user_action()
+        buffer.delete(start_itr, end_itr)
+        buffer.insert(start_itr, text)
+        buffer.end_user_action()
+
+    item = Gtk.MenuItem(label = "Prettify JSON")
+    item.connect("activate", on_prettify_json, buffer)
+    menu.append(item)