Change to respect DashClock extension visibility.

Update DashClock Extension support to respect the visible parameter of
extension data, so that invisible extensions are hidden from the card
list, reappearing if they become visible later.

Change-Id: I7767985659f24d5aed304ebbdc1e133d47f18d9d
Fix bug that displayed incorrect extension icons.

Cardslib caches the thumbnail image of each card in a Map. Previously,
we used the resource id of the DashClock extension as the key, but this
can result in a collision across multiple extensions. Change the key to
be ComponentName String + Resource ID or URI of the image.

Change-Id: I870ad155e64c42645240aac2c2984c336bae2fef
Merge changes I870ad155,I77679856 into cm-11.0

* changes:
  Fix bug that displayed incorrect extension icons.
  Change to respect DashClock extension visibility.