Settings : Toggle expanded desktop for navbar

If entering the navbar screen with expanded desktop enabled, the navbar
is not shown hence hindering the ability to use the panel

This patchset addresses that by disabling expanded desktop upon entering,
and re-enabling upon exiting if it was previously enabled.

Patchset 2 : Fix state issues

Change-Id: I2776cf971f8899d30a25c0bf6b418793153555fc