Process login, avoid duplicate nicks, display list of logged in nicks or invite message.

As a user who has identified themselves to the webapp, my identifier is processed and I am logged in
* If the identifier collides with another, add numbers onto the end until it doesn't
* Add user and identifier to presence system
* Display logged in content

As the first user logged in, I see a message that I am the only person logged in, and see an offer to invite friends
* Display web page with message suggesting sharing with friends to invite them

As a user, I see a list of identifiers of people who are logged in
* Get list from server
* Present list on the web page