Register hashchange event more cautiously.

Registering a callback for the "hashchange" event should not occur, before the $.deck plugin was used by the consumer. Otherwise it will be executed, even if there are no slides to actually operate on.

I experienced this behaviour (let's call it a bug) in an app where hash changes did occur before the deck plugin was initialised. This seems to be limited to single page apps, where a dependency can be loaded, before ```$.deck( ... )``` was being called.