Add RangeInput component

[lederer]

Overview

Add RangeInput component, a wrapper for <input type="range">.

X-browser styling is adapted from:

• https://brennaobrien.com/blog/2014/05/style-input-type-range-in-every-browser.html
• https://css-tricks.com/styling-cross-browser-compatible-range-inputs-css/
• https://github.com/darlanrod/input-range-scss/blob/master/_inputrange.scss

Checklist

• [x] Relevant documentation pages have been created or updated
• [x] Description of PR is in an appropriate section of the changelog and grouped with similar changes if possible
• [ ] Relevant status has been updated on the status page

Upgrade instructions

If there are any of the following in this PR, provide proper instructions on how to upgrade:

• [ ] Changes to the prop names or types of existing components
• [ ] Changes in intended behavior of existing component props
• [ ] Changes in the theme file's structure
• [ ] A required version bump to a non-dev dependency of the project

Demo

Notes

Also removed an unused import in Badge and tweaked the docs template to avoid errors in IE11.

Testing Instructions

• Fiddle with the RangeInput docs page via props and theme

Closes #124 Closes #202

[lederer]

Ready for another look.