Users, especially developers, may install freeciv-web alongside other
tomcat webapps. Be nice and don't hoard ROOT.

If so configured, use tomcat-manager to stop just freeciv-web and not
the whole tomcat server.

nginx.conf is an installation file, under the responsibility of the site
admin. The default upstream content already supports loading of several
virtual servers or apps defined under sites-enabled, so use that instead
of greedy full control.

Some more work may still be needed to really share nginx with other apps,
like declaring a server name or wrapping everything in a freeciv-web
specific location.

When stopping freeciv-web, remove it from sites-enabled and tell nginx
to reload its configuration, instead of stopping all of nginx.

Installing freeciv-web doesn't overwrite nginx and tomcat config anymore.