Trim the work done building an initial connection index

The watcher thread was calling the local master api to build a local connection index, complete with name, node, type info and xmlrpc_uri. The latter two aren't really necessary - we only need those for gateway flips/advertisements/pulls, so its a real waste of effort getting those values for every local connection.

Turned out this was criminal as it was causing xmlrpc spam between rosmaster and the gateway when under heavy load (lots of local connections). I've disabled this and we now run at about 10% of the cpu usage.

There are further optimisations that could be done, but this will be sufficient for now.

This closes #155.