improve frontend of emacs, ckeditor, tinymce, nicedit, meta and env functions

Improves in emacs:
- use htmx to send content to the controller
- show txt and formatted_txt content in the second panel
- show two tabs if "tabs" winix parameter is used
- add an option to show either one or two panels
- correctly resize the editor window (F11) when two panels are shown

Improves in ckeditor:
- use htmx to send content to the controller
- do not check automatically for ckeditor update

Improves in tinymce/nicedit/meta/env:
- use htmx to send content to the controller

while here:
- change PascalCase to snake_case in meta/env controllers
- update CodeMirror editor to 5.65.16
- udpate Showdown (markdown to html converter) to 2.1.0

winixd/models/itemcontent.h

@@ -233,13 +233,11 @@ public:
 
 	/*
 	 * parsed object content
-	 * IMPROVEME not used in winix yet
 	 */
 	std::wstring content_parsed;
 
 	/*
 	 * parsed content type
-	 * IMPROVEME not used in winix yet
 	 */
 	ContentType content_parsed_type;