Removed `contentSnapshotView` in favor of `contentView`.

Removed cell snapshotting in favor of moving the cell's contentView directly. All UITableViewCell subclasses should be adding their own subviews to contentView anyway (not to a cell directly).

See "Programmatically Adding Subviews to a Cell’s Content View" in "Table View Programming Guide for iOS".

https://developer.apple.com/library/ios/documentation/userexperience/conceptual/tableview_iphone/TableViewCells/TableViewCells.html