Top level - an activity with a list of all samples. The list is driven
by metadata collected from the manifest.
Second level - specific demos.
This allows:
* Clear labeling at the top-level of what we're demoing
* Much more flexible and scalable way to show multiple demos (instead
of one ViewPager)
* Consistent structure across all our support demo projects
Change-Id: I64a3b7788b14f0ac663be6616a2ec841ca53944e
