Added support for multiple gesture recognizers

This pull request contains 2 enhancements:
1 - Adds the keyboardPanRecognizer when the keyboard is shown and removes it when the keyboard is hidden. The idea is that keyboardPanRecognizer does not need to be monitoring for panning when the keyboard is not showing.
2 - keyboardPanRecognizer no longer cancels touches in view. This was preventing additional on-screen views from being able to monitor touches (e.g. a signature form), since the keyboardPanRecognizer was stealing all the touches.