Don't return early from performBatchUpdates with nil updates block
HotFix For issue #163
 - Supplementary views are now reloaded correctly while updating the CollectionView.

However initialLayoutAttributesForInsertedSupplementaryElementOfKind method should be implemented and used instead.
Merge pull request #205 from CitronEvanescent/CE_Issue163

HotFix For issue #163
Merge pull request #204 from neilkimmett/master

Fix inconsistency with UICollectionView's performBatchUpdates:completion: behaviour