Polish sizes and positions in intro screen
Implement buttons in the wordlist in the canvas

Instead of create a transparent div floating over the canvas,
draw the buttons in the canvas itself in the case of the app
running on android.
The svg are different , because are black instead of white.
A sound button is added accoreding to the design, but we don't
use it yet.
Fixes to the error bubble
Use linear gradients, no radial
Use a transparent background in the matrix

Need replace the white background by set the hitArea.
Also, add a hack to hide the superimposed letters in the first row,
after the animation, produced by a webkit bug on android
When a word is selected, apply alpha to the text too