New description

implement SVG support and fallback for non compatible SVG browsers

Old description

Images are blur on iPad 3 retina device. Actually looking at them closer, they are also quite blur on iPad 2 (for example the select arrow on the topic page or some activity icons like glossary or link).

I think we need:

• one folder for low resolution screen
• one folder for high resolution screen

Do you agree?

If yes I'll write an another issue + edit this one, we need:

• one issue for Josep to create both normal and retina icons
• one issue for Juan to choose the correct icon following the device (pixel density, screen size...)
  I'll mark them for 1.3.