Add some error codes

Fixes: https://bugzilla.gnome.org/710653
skydrive: Be resilient against errors when downloading

Having a valid stream does not mean that the request succeeded. We
should look at the message's status code to determine whether the
server threw an error an error or not.

In case of an error, we should parse the JSON and return the error to
the user.

Fixes: https://bugzilla.gnome.org/710653
Implement videos
skydrive: Implement thumbnail_file_id_to_stream

Fixes: https://bugzilla.gnome.org/710717