Make Apache configuration conditional.

Make sure that gitlab or gitlist won't prevent apache to start,
if those modules aren't yet compiled/installed.

M  .gitignore:
  Ignores 'gitlab/apache.cnf' (generated)
M  apache/env.conf.tpl:
  Replace GitLab definition with a conditional Include
A  gitlab/apache.cnf.tpl:
  GitLab Apache parameters, isolated in their own config file.
M  gitlab/install_or_update_gitlab.sh.tpl:
  Generate 'apache.cnf' for GitLab before starting all services.