ui: Make page tab-able

A table pile was added which allows to cycle through it's children by
using TAB and SHIFT+TAB.
For now only the main page is tab-able.

rhbz#918999
rhbz#917498

Change-Id: I5889716ba1ad2c9b232c5ae6f466f04f98f387a5
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>