Documented shadow map settings, fixed demo

Documented shadow map settings for directional and spotlights, and
duplicate entries removed. AlteredQualia's experimental cascaded shadow
code, currently broken, has been labeled as "experimental" - in the
long-term it should either be fixed or deleted. Fixed demo's (missing)
shadows by turning off cascading and using tight bounds on a standard
shadow map; added comments. Original demo on AlteredQualia's site still
works, if anyone wants to find the regressions and fix them. Original is
here:
http://alteredqualia.com/three/examples/webgl_morphtargets_md2_control.html