Application state management - launch

[jelster]

Adds the space-truckers application initialization logic and launch event handling.

Contributes to #32

[jelster]

Changes so far in the commits pushed:

• refactoring to extract the planet creation into factory methods
• design improvements via refactoring
• hiding of html ui on button click
• BJS loading scene and screen management

[jelster]

• Added a quick-hack fsm that uses function* generators to manage application state
• Main menu loads after initialization -- no cutscene yet to play
• THEME SONG!!! Plays when the main menu appears

#40 is an experimental branch that uses an NPM package to provide the state machine logic - @RaananW do you have any experience with libraries like this with BJS, and any reason to use or not use them?

[jelster]

Here's a diagram I drew showing the different application versus game states and how they interact. Many elements will have state machines of their own; I've omitted most of them to keep the big picture more clear