Updated slider and demo

Updated less file to be parametric, updated slider stiles and improved
the demo page.

Fixed the label not being centered when loaded hidden until after
clicking the slider.

Bug when use with other drag&drop framework, specify an event handler with specific type allow to not destroy other general purpose "onmouse" event handler (jquery-ui)

Fixes issues presented on hidden tab rendering.

Also adding a force re-render mechanism useful when using tabs.

- Performance
- Cleanup
- Documentation

When you drag one range pointer past the other, they 'swap' and you continue dragging the other one. However, if you did this rapidly the range would wander. This locks the values so that this wandering doesn't happen.