When moving files, `drive` should move he local files too

[tukusejssirs]

I think that when we move files (drive mv old/files* new/), drive should move the local files too. Even git mv works that way.

Currently, when I move some files with drive mv, I need to manually move the local files. When I fail to do that and run drive pull, I’ll remove the files from the old location and redownload then from Google Drive to their new location, which might be a quite long process if those files are large.

drive version I currently use is 0.3.9.1.