clock: update clock-common.h
clock: add clock-preferences.ui

This is same dialog window that is available in clock.ui except
small change - marked as composite template.
clock: add ClockLocationEdit

Add ClockLocationEdit that will be used for location editing
and/or adding new locations.

clock-location-edit.ui is created from clock.ui with small changes:
1) Marked as composite template.
2) Removed unused widgets.