Fixed android.app.Fragment callbacks from rationale dialog

[phcannesson]

Fix for issue #57.

I'm not 100% happy with the fix because it will only work on API > 17.

But do we really care about API < 17 as the permissions check at runtime appeared on Android Marshmallow?
In any case, we do the same API version check on file RationaleDialogFragment, so it would also need to be fixed.

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[phcannesson]

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[samtstern]

@phcannesson this change LGTM, thank you!

As for whether we care about API<17: No, not really. I think a larger refactor of this library is needed to make all the operations no-ops on API less than Marshmallow, since there are too many API and class checks all over the place. It's just technical debt that's accumulated, unfortunately.