Clean up deprecated code and fix multiple issues

- Remove deprecated markdown_preview plugin and re-wrote
- Renamed alt_provider.py under words completer
- Fix words completion provider logic and cache handling
- Fix container orientations (VERTICAL -> HORIZONTAL) and add Separators
- Remove unused Gtk imports from search_replace plugin
- Fix event creation parameter order in source_file.py
- Fix typo in source_view.py (_load_pretify_json -> _load_prettify_json)
- Refactor webkit_ui with new load methods and enhanced settings

plugins/code/search_replace/plugin.py

@@ -1,9 +1,6 @@
 # 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
@@ -62,4 +59,5 @@ class Handler:
         view: any
     ):
         logger.debug("Command: Search/Replace")
+
         search_replace.hide() if search_replace.is_visible() else search_replace.show()