Added ability to run feature modules independent from main app module

[sergevalevich]

This allows Instant App support [https://github.com//issues/209)],
running unit-tests for feature modules [https://github.com//issues/223]
and other issues [https://github.com//issues/224].

Here, Moxy always references to MoxyReflector by com.arellomobile.mvp package and generates
MoxyReflectorDelegate for each module.

In order to use Moxy, there is no need to follow instructions described on this page https://github.com/Arello-Mobile/Moxy/wiki/Multiple-modules

Now it is only required to add 1 line of code to each module's BaseActivity.onCreate, or App.onCreate or any place where feature module gets initialized : MoxyReflector.registerDelegate(MoxyReflectorDelegate.INSTANCE);

[sergevalevich]

Usage example for modules, which declare Application class:

class MyApp: Application() {
    override fun onCreate() {
        super.onCreate()
        MoxyReflector.registerDelegate(MoxyReflectorDelegate.INSTANCE)
    }
}

Usage example for library modules, which don't have Application class:

class MyModuleBaseActivity: MvpAppCompatActivity() {
    override fun onCreate() {
        super.onCreate()
        MoxyReflector.registerDelegate(MoxyReflectorDelegate.INSTANCE)
    }
}