[WIP] Use Javascript to render the frontend

This is a WIP commit towards using Javascript to render the UI.  It uses a mixture of ReactJS and some other libraries.

Lots of things are broken; this PR is effectively a code dump until I have time to work on this.  I'd love it if someone who's actually experienced with Javascript would like to pick this up and work on it.

List of broken / missing things:

- Popovers
- Table sorting (needs to be re-implemented in React)
- Jenkins test button