Move BBC button images to URI data instead of URL calls

This is a test to see what folks think about this ... it should be supported in ie8 + etc

Instead of URL calls to get the bbc button images, this converts them to URI data, which is just a fancy way of saying the image data is stored inline and contained in the CSS.

The result for the editor is approx 30 less http calls to get button images since the data is contained in the css itself.  We can apply this in a few other places as well.

(I did not convert the toggle image in preparation for @emanuele45 update to that)

Thoughts?