DeskClock: Move navigation bar to bottom

* Wrap the desk_clock layout into a LinearLayout so the Snackbar
  appears above the BottomNavigationView
* Change the icon tint and text color to reflect the changes for the dark
  layout
* Use a BottomNavigationView instead of a TabLayout
* Reorder imports - looks like someone didn't care before

Co-authored-by: Arian <arian.kulmer@web.de>
Co-authored-by: Jesse Chan <jc@lineageos.org>
Signed-off-by: Jesse Chan <jc@lineageos.org>
Change-Id: I780713dcbeb58256b2660a9631d48e5f7259fb11