Bug: icons not rendering properly

[kidwellj]

Map is currently showing default blue icons, and not rendering iconUrl: 'layer.png' as should be the case.

[kidwellj]

Also relation here to #10 and #7

[danhillcode]

I don't know how to do this with leaflet.marker cluster library could be a freelancer job I don't mind paying for it. Will be quick for someone who knows it inside out.