Bug 13791: Apache configuration files

Bug 13791: Apache configuration files

This patch adds an include to each VirtualHost definition (OPAC and Intranet)
and a variable definition, taking advantage of Apache 2.4.x features.

The instance name is reused inside the includes providing a simple way of
dealing with the apache <-> plack configuration.

A check for the right apache version is introduced, in the for of an IfVersion block:

<IfVersion >= 2.4>
  --- Plack configuration here ---
</IfVersion>

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>