64-bit fixes and delegate extension

Besides fixing 64-bit related compiler warnings and enabling to build for 64-bit, the main additions in this pull request is to allow calling user voice from a UIActivityViewController where the OS takes care of presenting and dismissing the view controller.

* A new getter `getUserVoiceContactUsFormForModalDisplay` which returns the user voice controller without presenting it. Granted, getters for other related methods would make sense to add, too.
* A new call back `userVoiceRequestsDismissal` which is called on the delegate rather than dismissing the view controllers through user voice.
* Made sure that the delegates are always called by factoring out the various calls to `dismissModalViewControllerAnimated:`.

Note that I wasn't sure what exactly the semantics of `dismissUserVoice` are and why it isn't always called. That's why I created a new method `dismissUserVoiceWithoutFlush:`.