how to handle styling on annotations layer?

[ischneider]

Right now, it's fixed to be 'red' for any geometry (with opacity for polygons).

If we wanted to reuse the interface we have, one issue is that the styling approach currently limits options by geometry type. So we would need a more open style type (that supports point/line/polygon styles - basic in this case?) and ensure the appropriate ol3 styles are generated by geom type.

I could see this also being initially limited to altering the color of a style that applies to all annotations.