Allow to write right-to-left in crosswords

[frncesc]

JClic Crosswords have three options for the movement of the cursor when a key is pressed: "go to the right" (this is the default), "go down" and "no movement at all" (you manually move the cursor using the keyboard arrow keys).

It will be great to have also a "go to the left" option, for right-to-left languages like Arabic or Hebrew.