Added support for asset deselection delegate messages.

* Added [ELCAsset assetDeselected:].
* Added [ELCAsset shouldDeselectAsset:].
* Added [ELCAssetSelectionDelegate shouldDeselectAsset:previousCount:].
* Implemented [ELCAlbumPickerController shouldDeselectAsset:previousCount:]
  to forward to parent.
Merge branch 'asset-deselect-delegate-methods' of git://github.com/bdeshong/ELCImagePickerController into bdeshong-asset-deselect-delegate-methods
Merge branch 'bdeshong-asset-deselect-delegate-methods'