This reverts commit 0b3a1849.

So far only used in two places, but it needs to be defined to changed there:
- server/lib/classes/db_mysql.inc.php
- interface/lib/classes/db_mysql.inc.php

- Updated version number to 3.0.5.4rc1

- Added function to detect the apache version to installer.
- Added support for apache 2.4 to vhots templates for ispconfig vhost and apps vhost in installer.

Undone the deletion of the config.inc.php file. It is intended that the file is there as dummy and gets replaced during installation.

config file which caused the restart of daemons to fail.

- replace double-quotes with single-quotes whenever appropriate
- fix indentation

Added the configuration variable $conf['demo_mode'] in the config.inc.php file. It disables the newly introduced demo mode which limits certain actions in the interface part of ispconfig: the demo mode can be used to run the ispconfig interface part as online demo.

- Fix some comments.