[work in progress] improve keyboard performance

[ngokevin]

The keyboard is 200 draw calls and lots of vertices/faces and raycastable elements.

Improvements:

• Animate fade in/out directly through ShaderMaterial versus .setAttribute. This cuts out all the .setAttribute overhead, animating tons of entities per frame.
• Get rid of text shadow entities. I didn't see them, and that cleans up 40 draw calls.
• Get rid of <a-rounded>, use slice9 component instead. The slice9 component is a normal plane, using transparent texture and UVs to get the rounded effect. This cleans up tons of vertices by rounding in material versus geometry.

To do:

• Merge all geometries
• Try to have only one raycastable element, and use intersection data to detect the key.
• Have only one plane for the key background, and just move it around whenever something is highlight.
• Use a single texture for keyboard versus dozens of text entities