Build modes.

[JSideris]

Rather than building to one giant library, the engine should have multiple builds.

• Client/2D: Contains core files, client files, p2.js, and pixi.js. Used for online or offline 2D games.
• Client/3D: Contains core files, client files, ammo.js, and three.js. Used for online or offline 3D games.
• Client/Core: Contains core files, and client files. Used for online or offline HTML-based games.
• Server/2D: Contains core files, server files, and p2.js. Used for hosting online 2D games.
• Server/3D: Contains core files, server files, and ammo.js. Used for hosting online 3D games.
• Server/Core: Contains core files, and server files. Used for hosting a server through which game clients may connect.