Added events/events and events/hotkeys modules

* Rewritten and decoupled most of the code to use events/events module
* Hotkeys can now be listened to independently by any module
* New hotkeys F1 (opens github project page), F2 (new game) and F3 (custom game)
* Added menuModule which handles function key hotkeys
* Renamed configurationForm to customGameModule
* Renamed some element's IDs in index.html and updated .css files accordingly
* game/main stops listening for keys when paused
* added new events `pause`, `restart`, `pause-toggle`,  `show-custom-game-module`