Easier form navigation

This pull request makes navigation through SCLAlertView form fields easier and more user-friendly. Hitting return on a field will take users to the next field, made clear by setting the return-key type on the field to *Next*, and hitting return on the last field will dismiss the keyboard so users can see any buttons/the rest of the screen once they are done editing the form, made clear by setting the return-key type on the final field to *Done*.