FIX (Gist editing): Fix editing,adding and renaming gists

Closes #119

Added a null check to renaming old files and updated a bad reference in
the view causing gist history to be invalid thus preventing further
edits to the gist.
Merge branch 'master' of github.com:Gisto/Gisto

* 'master' of github.com:Gisto/Gisto:
  UI(themes): update dark themes with latest UI changes
  UI(settings): fix settings screen is not able to scroll down