Ability for the action handler to get more info on the current file

This is required to fix video viewer app.  It needs file mime-type in addition to the filename to create video element properly.
Stable45 allows to get mime-type for the current file while processing the action with 

     FileActions.getCurrentMimeType();

while master implementation always returns mime-type for the last file in the files list instead.

This pull request reverts FileActions to the previous behavior.