Enabling media_browser_plus updates timestamps for all managed files

When enabling MBP, the file_move function is called. This has the (most likely) undesirable effect of updating the timestamp for the file so moved, breaking things like sorting files by the uploaded date.

An ideal solution would be to have separate uploaded and updated timestamps, rather than a single one, in the meantime MBP should attempt to work around this e.g. by stashing the original timestamp and setting it again after calling file_move().