refs #8221
Instead of serving our shared assets from a `shared/` folder, we move the file, which are used server side to `server/public`.
Adds a new `config.paths` entry: `publicFilePath` and renames the middleware to serve the files to reflect the changes.
Adds `404-ghost.png` images to be used by the server side rendered default template `error.hbs`.
fixes#4555
- There's no easy way to declare an XSL with the node xml module, so I
needed to move the declarations to both be strings
- Ideally the code to serve the XSL would also be inside the sitemap
module, but I think we need to refactor a bit to get there easily
- Added the XSL from #4559, with minor amends to make the tables and urls
display correctly
