Enable Contribute page to respond to screen size changes (#232)
* Add clean and serve scripts
* Improve code highlighting on contribute
* Ensure we have the latest prismjs and prism-react-renderer
* Shorten example description to make it easier to read and reduce screen sizes where overflow is required
* Fix JSON5 syntax highlighting
* Specify markdown sytnax highlighting for front matter samples. Markdown front matter highlighting will come to PrismJS in the next version (https://github.com/PrismJS/prism/pull/2634)
* Trim whitespace and newlines from the end of code samples
* Add scrollbars to code examples
Enables the Contribute page to shrink according to screen size
* Allow code examples to be scrollable by keyboard users
* Disable eslint warning for tabIndex on pre element
