TMQuiltView should cache the heightForCellAtIndexPath

[rickmak]

TMQuiltViewDelegate have protocol: - (CGFloat)heightForCellAtIndexPath:(NSIndexPath *)indexPath;. And it result a performance issue if the height need a calculation according to cell content. The currently implementation simply request the method every time it layoutSubView(though rectForCellAtIndex).

Like UITableView, it should call once for each indexPath and cache it. Prevent re-calculation during scroll. The cache should be clear after the user call follow method:

- (void)beginUpdates;
- (void)resetView;