Add interactivity for color scale sliders

[Nate Baldwin]

For each ratio swatch input, needs to integrate with slider.

• When focused, slider must become visible
• Slider must be interactive when visible
• Slider should use previous method of input, where slider represents value of current domain of gradient. This domain value passed from colorArray, calculated ratio returned as input value

This will enable users to move a slider as an alternative to entering numbers into the contrast ratio swatches.