Webgl text rendering

[dy]

Now labels in webgl mode are just span elements. That drops FPS in firefox and iphone. We could try doing some cache-texture in canvas2d and forward it to webgl whenever cache changed. Worst case it is going to be like gl2d. Best case it will avoid moving texts at all. That should be a separate component, like gl-render-text, but without texture2d wrapper as an output - just simple renderer.