Invisible activity is always created on background

[Serchinastico]

When asking for permissions, the invisible activity is always created, this might cause some issues if Dexter is called from the onCreate or onResume methods of your own activity (as it will force another call to onCreate & onResume once the inner activity is dismissed). We should only create the inner Activity iff ActivityCompat.requestPermissions is going to be called.

For calling checkSelfPermission we should use the provided application context.

[Serchinastico]

Duplicated #47