Retina toolbar icons

[tmcw]

Would be great to have 2x versions here. Is there an SVG version of the spritesheet so I can do a pull request?

[jacobtoye]

Requires the latest Leaflet changes that adds leaflet-retina to the container div. The previous spritesheet was a hacked up mess with parts of Glyphicons and shapes. The SVG is exported from Illustrator but it should be fine (tested in Inkscape).