Fix ordering of adding long press gesture recognizer

I'm seeing repeatable crashes upon `dealloc` in the `UILongPressGestureRecognizer` associated with LXReorderableCollectionViewFlowLayout.

I believe this stems from the order in which LXReorderableCollectionViewFlowLayout sets up its gesture recognizers on the collection view in `setupCollectionView`. 

Specifically, my collection view does not have a default long press gesture recognizer, so when `setupCollectionView` calls `-requireGestureRecognizerToFail` to attach it to the default long press recognizer, it actually ends up requiring itself to fail and thusly (I'd guess) prevents itself from being deallocated. 

The fix is simple: don't add the new long press gesture recognizer to the collection view until after any other `-requireGestureRecognizerToFail` dependencies are set up.