Hide the template thumb on phones

Tracker:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33666&start=0
Update default.php
Update default.php
Merge branch 'patch-20' of github.com:zero-24/joomla-cms into zero-24-patch-20
Merge branch 'zero-24-patch-20' into staging