Add visualisation tool to a new page

[stevenday]

Integrates https://github.com/openownership/visualisation-tool into the OO site as a new page where people can visualise BODS data.

This is mostly based on the demo pages in that repo, but with some additional features to improve the usability (since those demos are meant to be a minimum viable version).

In particular I've added:

• A legend
• Some error catching for bad data/invalid BODS
• Auto-draw on paste
• Some styling to match the OO site and some css to fix compatibility issues between the two (mainly around responsive images which mess up the icons)

Process

• Document (and build) a window library version of the tool (i.e. not a UMD or CommonJS module)
• Rework the demo index.js code so that we have something similar which uses this version, not Webpack, document this for re-users
• Figure out how to make the path to the images folder configurable and document this. I think we'll need to use https://webpack.js.org/loaders/file-loader/#posttransformpublicpath but where can we actually set the path? Can we somehow configure the global object or pass a param to executeDraw?
• Create a new jekyll layout for this page or figure out how to selectively include it in the existing visualisation one just for this specific page
• Add the right library and images folder to the assets folder
• Include the CSS too
• Style the submit buttons, etc
• Look at basic UX improvements:
  • Add a key to explain what the arrow colours mean visualisation-tool#19
  • Validate input to alert the user when we can't parse it as BODS visualisation-tool#18
  • Automatically draw on paste of data visualisation-tool#31
  • Flip ownership and control in diagrams visualisation-tool#28
  • [ ] Support for vertical diagrams visualisation-tool#34 Too tricky with the time left