View is removed from superview upon completion of tour

Here we go. Revised code from the previous pull request.

I took some of your suggestions, and instead of worrying about the alpha being below a certain threshold, I've implemented  ```-(void)finishIntroductionAndRemoveSelf```, which calls the correct delegate method and removes the view from it's superview. This method is also called in the completion of the ```hideWithFadeOutDuration:``` method.

I wasn't sure how to remove the previous commit, but the latest commit of mine will overwrite the changes made in there anyway.