Adding keybindings to timepicker (Bug #1267239)

Can now adjust hour/minute values with keyboard

The key bindings added for timepicker:
(to avoid clashes with existing key bindings)
ALT+UP: Move hour slider up one step
ALT+DOWN: Move hour slider down one step
SHIFT+LEFT: Move minute slider down one step
SHIFT+RIGHT: Move minute slider up one step

Change-Id: If073908f070eada92dfa4d010f28ed53f7ac3b04
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>