Improve icon-sprite-webgl example code
Improve icon-sprite-webgl example code

Should load slightly faster now by adding the source only after all
features are available, this avoids dispatching the addfeature event
for each of the 80000 features.
Use webgl tile layer for the background so the canvas can be shared
between both layers.

openlayers/openlayers,bjornharrtell/ol3,openlayers/openlayers,ahocevar/openlayers,bjornharrtell/ol3,stweil/openlayers,openlayers/openlayers,oterral/ol3,stweil/openlayers,oterral/ol3,bjornharrtell/ol3,ahocevar/openlayers,ahocevar/openlayers,stweil/openlayers,oterral/ol3