added a cache to the IdentityManager, changed its signature, modified when and where the author is stored

made the author creation single-threaded again in the LifecycleManager, removed redundant code

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

Modified the project structure, removed module extension and went instead for a non-complete core dependency graph

Semi-encapsulated the core/api dependency graphs and created a proper structure to load eager singletons

The text of the startup failure notification is unhelpful due to lack of
space. Touching the notification now launches an activity that gives details
of the problem and what can be done about it.

Closes #38

Very important stuff.

See
https://developer.android.com/guide/topics/ui/notifiers/notifications.html#NotificationResponse

If the schema of the database is incompatible with the schema expected
by the code, the database throws a DbSchemaException. LifecycleManager
indicates the error to BriarService, which uses HomeScreenActivity to
show a notification and quit the app.