Add some object-state methods on NITableViewActions

Adds a couple of methods to NITableViewActions to allow callers to know which accessory type or selection style the NITableViewActions instance would set for the cell for a given object. 
This is required because callers may need to know if accessories are present when calculating layout such as the height of cells, but the only way for layout code to find out if they have accessories at the moment is to call tableView:willDisplayCell:forRowAtIndexPath:, which has the side effect of lying to the viewcontroller about which cells are being displayed.