Move integration tests into their respective modules
When we switched from Guice to Dagger, we put the integration tests in an Android module because the android-apt plugin didn't support Java modules. An APT plugin that supports Java modules is now available, so we can move the integration tests into their respective modules and remove the briar-android-tests module.
The "idea" plugin should also be used so that Android Studio recognises the generated classes: http://stackoverflow.com/a/37963784
Subtask of #136 (closed).