Add dogfood variant

[JakeWharton]

Include Telescope + first-run tutorial.

[JakeWharton]

We do this as a build type, but only out of laziness and a desire to avoid combinatorial explosions. Here, however, I think we should do it as a product flavor where the flavors correspond to the "production" Play Store and "internal" Play Store (or whatever distribution mechanism you'd use).

This will create debug and release dogfood apps. For now we'll only share Telescope, but this will be a good test bed for sharing a drawer subset in the future and developing a way to make it modular.

[JakeWharton]

😢 http://b.android.com/162285