trebuchet: custom home

Change-Id: I4faee66580ab0e41ee8e8bcbd79ce680d45bce97
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>
Add a custom home screen to Trebuchet.

Scrolling to the left will now open a custom home screen that can be
used to display information provided by the system or third parties
via an API.

Change-Id: I62991c0634b686ca875d04fa118695050731ba7e