Retroactively add EffectiveNavigation and TabCompat sample code.

This sample code was launched with the Implementing Effective Navigation and
Creating Backward-Compatible UIs training classes, but the source was never
added to AOSP. This retroactively adds the source, unmodified.

Change-Id: If6face5a0548107f7fd273e466b1ced2790f4f3a
49 files changed