sysUI: statusbar clock

fixes following bugs:
- lockscreen will hide clock by default to avoid a double clock, but every
  minute the clock updates it would show again
- hide clock would hide the big clock in the tablet notificatiopn panel
- tabUI notificationcenter would not hide the statbarclock (double clock again)

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/policy/Clock.java