2D canvas rendering support

[Valtteri Heikkilä]

Add support for 2D canvas rendering. It would look same as NTSC & TV emulation turned off. Direct RGB lookup can be generated from existing lookup texture data. It would also look better to split NTSC emulation lookup generation code to a separate file...

Pros:

• 2D canvas works on more browsers than WebGL.
• Provides fallback if WebGL is not supported.

Cons:

• NTSC & TV emulation are disabled for 2D canvas.
• Possible complexities in disabling/hiding UI controllers.

[Valtteri Heikkilä]

Added in 0.3.1-alpha.