Add option to select temperature unit

Added a menu in the weather settings to select the
temperature unit. This setting will be visible only
if the user has at least one weather service provider
installed.

The weather settings layout was refactored to make room
for this new preference

Change-Id: I5e9f206573e0ff95fcee31a010b52530a907acc6
TICKET: CYNGNOS-2605
(cherry picked from commit 215d4402)