initial svg icon support

@bartvde 

Main thing to note is that icon fetching is async but in the ol3 style building we're using a synchronous API because it seems like there is no way to modify the style once built - like trigger the fetch, then update the style on completion.

Another approach would be to ensure that any async loads trigger the style refresh.

The current approach works fine but requires the remote resources are resolve prior. This currently is safe as the 'default' icons are all resolved on page load but we'll have to eventually deal with the case when they are not.

I also put ol3 non-debug build back in the style example to avoid using 'hidden' API :santa: