Add react-native-slider props

[RageOfJustice]

Hello. Could you add some props from react-native-slider (GradientSlider uses it) such as onSlidingComplete? It would be useful to save color to the State (Redux) on silde end.
Thanks

[hectahertz]

Sounds good to me! I'm not working on this project right now but feel free to open a PR 😄

[eduardomrodrigues]

Hi, @RageOfJustice ! Can I take that for me?