added shuffle

- shuffle rule, command and logic (using
seedrandom.js)
- client creation functions are now registered with Game (to support
custom clients)
- HumanClient split from Game, now independent
- HumanClient supports the MoveRule (at least for one card), and uses
interact
- better event management in Interact, off can disable events, and
events are kept after disable(), to be automatically re-activated on
enable()
- facedown is a basic property of the layout, if true or false, then all
children have facedown = layout's facedown, otherwise the facedown flag
of the child is left untouched
- loveletter.html renamed to loveletter_common.html (as this is the
common screen of the game), interact code has been removed (this is now
handled by humanclient)
- created loveletter_debug.html to provide the game in an iframe
- the proxy will call the game setup func, as it owns the board
-