Support for Dagger 2

* Mortar is now agnostic of the dependency injection library.
* Backported Dagger1 support into a small module: Blunt.
* Added a module for Dagger2 support: Sharp.
* mortar-sample still uses Dagger1.
* mortar-helloworld now uses Dagger2.
* Removed support for runtime graph validation with Dagger1.
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