On-The-Spot: Underp Safe-Headset one once for all and code cleanup:

After Gif support, context managing went derped resulting in the old NPE.
Valter's fix restored all the contexts that are used within system one that
we need just to read&write to system, but dialog's builder needs one created
by the ThemeEngine.

* Fix dialogs not being themed:
  Pass themed context only to dialog builder by crating one when needed.

* Cleanup implementation:
  Restore all normal system contexts and add an helper method to generate
  a theme context to be used by AlerDialog.Builder() for pulling themed resources.

PS3: Miscs
PS4: Code cleanup
PS5: Commit message cleanup

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>
Change-Id: I1e3f9dce7dd448306db0364ab6e1ff8a71160729