Allow a server option to be passed through to sockJS via DDP.connect

This simple change gives us the ability to set the server component of the sockjs url.  The benefit is that we can then have our proxy route to an appropriate server based on the url.  It allows us to make sure all users within a certain group (organization in our case) are routed to the same server, providing them with real-time updates instead of a 10 second delay, without depending on oplog.

Without specifying it, sockjs default to using a random 3 digit number.  e.g. the 518 in: wss://example.com/sockjs/518/es6gmosh/websocket