PowerUI: Remove the fallback dialogs.

- Low battery notifications are now always notifications, even
  if not HUNs.
- Remove obsolete dialogs used only as HUN fallbacks.
- Extend the default HUN timeout to 10 seconds and remove the
  ongoing hack for the warning notification.

Bug:17070231
Change-Id: I29069c3d90dcca6f9bce512e5a0ccbd983704de5