Fixes for init/scrambleBoard. Button experiments

Initialization was not correct before. Have to reset board and cellVal
in initBoard().
Buttons should be animated. Experimented with tutorial
http://webdesignerwall.com/tutorials/css3-gradient-buttons
Handling of buttons (gradient, hover, active) ok

The concept works. So far the values are only correct for webkit browser
==> other vendor lines for gradients have to be adapted.