Application launch and initialization

[jelster]

When a user clicks the launch button after navigating to the default landing page, the application transitions from the initial indeterminate state to the Initialization state. Comes after #31

Requirements needed to close this issue:

1. • HTML elements should be removed or hidden
2. • The browser window should enter full-screen mode (may require user interaction to accept request)
3. • The loading UI should display
4. • Assets are loaded
5. • Loading UI is hidden
6. • The opening splash screen / intro (attract) scene plays
7. • The title theme music starts
8. • Main menu appears, transitions to front
9. • User controls are enabled, allowing menu options to be selected

[jelster]

WIP Playground snippet - here - incorporating it into the code as I go

[jelster]

closed with #45