Add rudimentary shareousel support to ShareTest

Functionality and caveats:
- Shareousel can be enabled whenever sharing media.
- The photo roll always consists of the 8 bundled images from ShareTest.
  You can either start with one selected or all of them.
- Setting the focused item doesn't seem to work properly, but I'm likely
  using the API wrong.
- Each time you toggle an item, a random set of custom actions are
  generated.

KI: Switching to non-image media type will break this impl

Bug: N/A
Test: Manual usage of ShareTest app.
Change-Id: I3d48ab95be3a8b503ad2f02806ff232e1a6819ef
6 files changed