Complete work on configuration.rst

- [x] search.facets.limit and search.facets.limits, one of these is wrong
- [x] FileStore-related options missing, see <https://github.com/okfn/ckan/blob/master/ckan/config/deployment.ini_tmpl#L245> and <https://github.com/okfn/ckan/blob/master/doc/filestore.rst>
- [x] `extra_template_paths` and `extra_public_paths` are _not_ legacy
- [x] `ckan.template_footer_end` _is_ legacy

Please add any other missing or wrong stuff to this page.

Please turn this issue into a wip pull request, don't make a separate pull request, to keep it all in one place.