Attach the status icon URL and etag to the Icon instance

Ignore-this: 7152ba0024163eb15b7ba83fa56bdb4c

darcs-hash:20130715102843-b22ec-93ec431e3238f44d3591ae2be12a025f8c5597b2
Renamed uri/relative_uri to url/relative_url on XCAP Documents

Ignore-this: e88fccabd0f0857928a5f5671b579fa6

darcs-hash:20130715112401-b22ec-4213b7927601164b630fd63767452c28a08df5d2