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

Also fixed a couple of bugs.

This also adds a setting allowing people to turn blog post notifications off.

Closes #488

This replaces the custom layouts in the navigation drawer with a
`NavigationView` and adds a menu entry for Blogs.

A Main Blogs fragment is added that holds a `TabLayout` and a
`ViewPager`. Five tabs are already added, but they just have a single
placeholder fragment that is to be replaced by the actual fragments.

Closes #409

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

and stay in it when configuration changes

Closes #370

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

Includes code from https://github.com/consp1racy/android-support-preference
License: Apache License v2.0