Fix hidden "Remove" and "App info" buttons in landscape

On grouper the "Remove" and "App info" buttons are not visible if the device
is in landscape. Layout the children of the drag_target_bar vertically to
fix this.

Fixes: https://jira.cyanogenmod.org/browse/CYAN-3744

Before: http://i.imgur.com/SHMTUjK.png
After: http://i.imgur.com/4JeJi8k.png

Change-Id: Ie8a9a799fa89bf8ad233202da10c808ab65a66a9