Ajax load bar on click "Lock/Unlock" in the file tree

I thinks we should add some progress bar by "lock/unlock" button because I suppose response can take a long time in some cases and it can be annoying for users. Now, locally, it happens immediately and of course the is no any problem.

@jschatz1 This issue is more like a discussion place. I'm not sure what should we do exactly and how. Please decide :)

mentioned in merge request !440 (merged)

Nice job @vsizov