Search results can become odd without the country search
terms, so make their inclusion a mandatory part of the
setup.
Also adds a new configuration variable to restrict the
languages taken into account by Nominatim.
Basically leaves the part that needs to be done by the automatic
vagrant script in the bash script and moves the remaining part
into an OS-independent md file.
Also fixes some of the instructions for CentOS. Now almost runs
through (some minor issue with permission remains).
