Change build targets for settings tests

1. Split existing tests into fully automatable (unit/) and not fully
automatable (app/)
2. Revert previous changes to test runners on app/
3. Fix some typos in readme

This will enable us to add the fully automatable test target
SettingsUnitTests to the continuous integration tests on the platform.

Change-Id: I0f42c59fde84891e4bfc379150c2f0c61ce1329f