Switched AppBus for ResultHandler, Controller for Helper. Added the basics for LifecycleControllers and implemented it for BriarActivity and NavDrawerActivity

This also introduces constants for the GROUP_ID, FORUM_NAME and
MIN_TIMESTAMP as they were used for the two buttons.

Closes #313

This closes #204

Thanks to the team that audited CryptoCat for this idea. :-)

Very important stuff.

Fixes bug #42.

Hopefully this gives users a better understanding of whether their
messages and contacts are accessible than "Briar is running" and "Quit".

This avoids a possible problem where the app expires while it's running
and every activity shows the expiry warning, leaving the user with no
way to quit.

This will allow any activity to show the expiry warning and password
prompt, and to start and stop BriarService.

SplashScreenActivity, SetupActivity, ExpiryActivity and PasswordActivity
are special cases.