Call onNext and return handled response

[martynhaigh]

With the current implementation, the observable won't be triggered if you want to return false to the View.OnTouchListener onTouch method. This change means the onNext method gets called on the observer and the onTouch method has it's return value set as sepcified in the passed in Predicate

[JakeWharton]

This is a behavior change that would only be suitable for a major version. Feel free to join the discussion in #204.