urwid: Add attr to footer

Previously the footer was sometimes hidden due to missing attributes
(which lead to the text beeing drawn in the same color as the
background).
Now the default text color is used.

Change-Id: I8b6d8c80ac516471b2e71addae15501a279ae7e5
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=982528
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>