Added file context popup on long press

On long press, a pop up menu appears that gives the file options (open save, share, details, etc).


This pull request is mostly for the pop up itself, only the menu items that were already implemented (open, add to favorites, etc) are implemented.

This has a generic pop up implementation that should be able to be used elsewhere.

((I also switched the Favorites Item View to use the File Item View instead to DRY it up a bit))