Add documentation on writing JavaScript extensions.
Review Request #8524 — Created Nov. 5, 2016 and submitted
Something our Extending Review Board documentation has been missing for quite some time is a guide on how to write JavaScript extensions, and overviews of the (few) hooks we have available. This change introduces these guides, providing examples of the various ways that JavaScript extensions can be specified, configured, and written, along with things to watch out for when writing these.
Built the docs and went through them, checking for errors, broken links,
and bad code samples.