Add Customizeable faces

[PommesSchranke]

• Customizable faces
  apache-mode now defines it's own faces. That way, faces may be
  customized just for the purposes of this mode without affecting
  your entire emacs session.

• Highlight unknown

  s and variables, too (default: font-lock-warning-face)
  This was done for two reasons:

  • Firstly, errors become more visible in apache config files.
  • Secondly, you may define the '...-unknown-...' faces to
    match the other faces, such that you may use this mode to
    edit files with apache.conf syntax and have syntax highlighting
    there (https://metacpan.org/pod/Config::General for example).

[zonuexe]

@PommesSchranke Thank you for your contribution.
I will check it later and merge it. Adjustments may be needed for the matcher.