Add a text description in the demos

[NathanLovato]

What the shaders do and how they work isn't always self-explanatory, especially as some are there for learning purposes or are low-cost variants of more expensive real-time effects, like the pre-baked glow.

We could use a UI component that gives some info about the shaders, available in all demo scenes. It can be part of a base scene that all demos inherit, or exist as a reusable component. See #1 and #2

[Razoric480]

I've added first pass for the 2D demos. Will refactor the 3D scenes next.

I went with the re-usable scene route, which is what was used in the steering framework demos.

[NathanLovato]

Perfect, thanks!