[syntax_highlight] Port Syntax Highlighting Plugin
I've ported the syntax highlighting plugin from old Gajim 0.16 to 1.1. Along the way I cleaned up some code and added new features:
- No more unnecessary text deletion and re-insertion
- special formatting (ASCII and others) now possible when not in code block
- more control over how the code looks (font, highlighting, background color)
- Code preview in settings
Edited by Philipp Hörist