Improve gesture recognizer spec helper

This improves the usability of the UIGestureRecognizer spec helper by removing the need of whitelisting the target's class. By doing this, the `-recognize` method also gains the ability to trigger segues hooked up in a storyboard.

Ideally this patchset would be tested on real-world test suite that uses the gesture recognizer spec helper more pervasively to make sure that there are no unexpected regressions caused by removing the whitelisting mechanism.

Thanks to @xtreme-daniel-crampton for taking a few minutes to pair with me while starting this work.