Allows for the deleting of files when editing a gist.
Whenever the users deletes a file block on the gist page,
the server will notice a missing file and send this as a removed
file to github.
Merge branch 'feature/ux' of https://github.com/sntran/gists.io into feature/ux

Conflicts:
	lib/gistsio/gist_handler.ex