Include the BIP21 prefix in the /health endpoint

[isaacvr]

When creating QR codes and URLs for requesting coins, the content is similar to this: skycoin:[address]. That is a simple example similar to coinName + ':' + address, but there could be coins with complex names (maybe with more than one word) and in that case just using the coin name may be a bad idea. Because of that, it would be good to add the URL prefix to the /health endpoint.