added delay and label plugins

- new delay plugin to force the server to wait
- new label plugin for setting labels on cards or locations
- supported rules for guard and prince
- game now has turns, with winner tokens
- game has winning state
- changed offsetWidth, offsetHeight to getComputerStyle because it is
faster, and it is still valid even if the element is not displayed
- added a grid display type
- added more error messages, to trap common problems