installer: default to using apache-vhost frontend

https://trello.com/c/Wqm0PpCz/211-5-deprecate-the-mod-rewrite-frontend-plugin-ose-2-2
Merge pull request #469 from sosiouxme/enterprise-2.2

installer: default to using apache-vhost frontend
install: mod-rewrite frontend deprecation notice

It is now listed in RECENT CHANGES (which we really hope users will read)
that mod-rewrite has been deprecated in favor of vhost frontend.
Merge pull request #470 from sosiouxme/enterprise-2.2

install: mod-rewrite frontend deprecation notice