Problem was that objects could be added to WebGLRenderer's internal render list only once (because of `webglInit` flag).

Now there are two separate internal states (`webglInit` and `webglActive`) so that object can be initialized just once (expensive operation) but added / removed from the scene many times (cheap operation).

Also removed unused material Sprite parameter.

This buggy pattern ("something = parameter || nonzero value") exists at more places though elsewhere setting to zero doesn't make that much sense (e.g. in geometries).

Not sure if we should change it everywhere to proper pattern ("something = ( parameter !== undefined ) ? parameter : value").

Maybe it would be good for establishing habit. I remember fixing this buggy pattern long ago but it just keeps popping up.

Also shortened a life cycle for particles in shapes example. Still it gets about 10 fps slower with time :/

No need to computer Beckmann texture every frame, once is enough.

Added renderer.getClearAlpha. Extended RenderPass to be able to use custom alpha clear. Fixed UVs in UTF8Loader.

Committed deployment version by mistake.