Flip select indices

This update adds an indexPaths parameter to func animateCells.

func animateCells(animation: TableViewAnimation.Cell, completion: (() -> Void)? = nil)

func animateCells(animation: TableViewAnimation.Cell, indexPaths: [IndexPath]? = nil, completion: (() -> Void)? = nil)

This change is non-breaking, since indexPaths parameter is optional. Your old code should continue to work as it did before.