Use AutoLayout in SWHUDCollectionView

![i-have-no-idea-what-im-doing-dog](https://f.cloud.github.com/assets/544011/2480480/3abc0f6e-b0be-11e3-9cd4-e304da105878.jpg)

It would be awesome if someone could have a look at `SWHUDCollectionView`'s implementation of `updateConstraints`.

This is part 2 of #63.