CM6: Fixed a range of issues during browser testing

CM6: Fixed a range of issues during browser testing

- Fixed some keybindings not running as expected, due to some editor
  defaults overriding or further actions taking place since the action
  would not indicate it's been dealt with (by returning boolean).
- Fixed spacing/border-radius being used on codeblocks on non-intended
  areas like the MD editor.
- Fixed lack of BG on default light theme, visible on full screen md
  editor.
- Fixed error thrown when the user does not have access to change the
  current editor (Likely non-cm related existing issue)