WBNoticeViewSlidingMode introduced + bug fixes

Hello and thank you for making NoticeView

I've added the ability to slide the notice from the bottom up without braking the existing API. I think NoticeView is the best looking on the market so I extended it because I needed a notice view that could stick to the bottom for http://kanbana.com/ipad

I've added the feature as a property like this:

    WBSuccessNoticeView *notice = [WBSuccessNoticeView successNoticeInView:rootView title:title];
    notice.slidingMode = WBNoticeViewSlidingModeUp;
    [notice show];

I've also fixed this issue https://github.com/tciuro/NoticeView/issues/28 

and an error when you tried to dissmis a nonSticky notice manually

I hope you'll merge this into your main repository and update the pod. I use Cocoa pods so I hope to use NoticeView as a pod in the future

Best Regards
Troels Richter
http://twitter.com/troelsrichter