Use Gio.content_type_guess to identify mime type - Fixes #4715

Replace the use of a custom implentation in SugarExt

Signed-off-by: Gonzalo Odiard <godiard@sugarlabs.org>
Implement mime.get_mime_parents using python

This is the only method pending implemented in c,
then we can remove seven files previously used.

Add a test for a corner case untested previously

Signed-off-by: Gonzalo Odiard <godiard@sugarlabs.org>
Remove c implementation of mime methods

Signed-off-by: Gonzalo Odiard <godiard@sugarlabs.org>