Username option on initialization

[markgeraty]

Add an option username to the options passed into the client side initialization.

So that would leave us with

api.initialize = function (options) {
  client = options.username || getCookie('username') || <random_number>;
  ...
};

We may even just want to get completely rid of jibe checking the username cookie altogether. If people want to have the name stored between sessions there, that's fine, they can just check the cookie and then act accordingly themselves?

@joshgordon @enriquecaballero @cicavey @ctsmith95 Thoughts?