Change: Removed favorite button from file list and added it in the sidebar

We've removed the favorite star button in the file list and added instead a functionality 
to the before non-working star button in the file's sidebar. We also added a new action in 
the file action dropdown menu which allows you to toggle the favorite status of your file.

https://github.com/owncloud/web/issues/1987
https://github.com/owncloud/web/pull/3336
