Extends userguide page for simplicitySelectSlider to describe the new
dual-handled functionality.
Fixes Simplicity classes.

https://github.com/t11e/simplicity/issues/31
Fixes styles for the getting started example.
Fixes the simplicityFancySelect userguide page to work again.
Updates the changelog notes about the CSS changes to document the actual
changed classes.
Adds CSS note to the improvements section of the changelog.