closes#9749
- disallow indexing of /p/ in robots.txt
- add meta robots tag to preview pages
- robots.txt wont' be applied for blogs not mounted to the root (i.e. https://example.com/blog/)
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`.