[fix #2530561] Slider updates. Skin assets now live in /build/slider-base, not /build/slider. Updates to Slider examples.

Duplicating slider-base skin files as slider skin files to support skin override in YUI config. Minified non-sam skin slider.css and slider-base.css (sam is done by the build process).

Adding skins sam-dark, round, round-dark, capsule, capsule-dark, audio, and audio-light. Not discovered and deployed by builder yet, so build/.../slider.css is not compressed except for sam.