Fix pointer's incorrect position setting

See merge request !1

#534

Provides the option to label slider(s) for screen readers using either a direct label via
`aria-label` or as a reference using `aria-labelledby`.

fixes issue #492

Ensure translate function behaves the same for keyboard commands and drag events as mouse clicks by
ensuring the model is applied before updateHandles is called.

Thanks to this refactoring, it's now easier to overwrite the style

close #479

* feat: Add selectionBarGradient option to customize the selection bar

Add selectionBarGradient option which create a linear gradient for the selection bar. The option

accepts an object that contains `from` and `to` properties which are colors describing the gradient

* Add tests to the gradient feature

* Handle vertical + reverse case

close #472

* prevent angular being loaded twice when using with browserify

* build release

* Add Math.round for transform position