Reorganized menus

* Subtitle menu can change all sub properties
* File List context menu can change all sub properties + apply pfiles
* Subtitle Editor context menu edits current subtitles (e.g. adds/removes subtitles, copies/pastes,
  changes times, etc.)
* Stub actions for SubtitleEditor context menu added
* All menu actions now have a shortcut (underlined letter - dunno how it's called)