Add support for input fields that use UITextView

I just used your UITextfieldScrollViewController class, and it works awesome! I made a slight change to support UITextView input fields as well (for multi-line input), and thought it might be a good idea to open a pull request to your repo.  The change in the xib file is just to add the UITextViews (see screenshot).

Thanks for this nifty utility!

![textview](https://f.cloud.github.com/assets/5897977/1507466/37dabd74-4983-11e3-9a7f-7c26c701f002.jpg)