renames _updateTemplate to _initialiseTemplate in GamePage
changes Glicko.DEFAULT_RATING to jsonchess glicko2Defaults.RATING in User
minor style change - changes direct return of promise to assignment in User to avoid multiple exit points
returns a Promise from User.register()

forgot to do this while implementing the promise changes before, so there
was a typeerror on register().then()
disables Rematch button on GamePage after clicking it

this is just done by "has the user clicked the button yet" as opposed to
looking at the Game, as the server doesn't send anything to the rematch-
offerer.
checks for existence of /login promise before trying to resolve it in /login/success
handler in User.

(for /register the code just assumes there's a promise if it's getting that message
back, but registering logs you in as well so login() won't always have been called
before /login/success comes back)