Cloudmade discontinued free product

[danswick]

This was covered in the "updates" issue in a roundabout way, but probably deserves its own issue thread. Now that cloudmade has switched to an enterprise model (see leaflet issue here), crosslet could use a straightforward method for pointing to tiles from other providers.

For my purposes, I've just removed all the cloudmade-specific properties in crosslet.js and index files, then linked to some MapBox example tiles, but this might not be obvious to others.

Thanks for making a great little utility. It's been hugely useful thus far.