4.2.0 Drag & drop sorting for all playlists

- Drag & drop sorting for all playlists
- Cleans up unused files
- Fixes 'grunt test'
- Fixes the "default" album cover not showing up after building with 'grunt'
- 'grunt' now also minifies all CSS files
- dist/vendor.min.js and dist/vendor2.min.js are now merged into a single file
- adds 'grunt deploy'. Deploys dist/ folder on a test server using sftp
- Removes unnecessary Grunt tasks & plugins
Fixes #178. Replaces $rootScope.SelectedAlbumSort with SelectedAlbumSort

Thanks to brb-at (https://github.com/brb-at)
Bumps up version to 4.2.1, modifies 4.2.0's changelog.