Impoved the software update function to enable the installation of apps like phpmyadmin into the apps vhost.

- changed GRANTs for slave servers on multiserver setups
- added option for clients to change path of ftp users (inside webroot)
- extended software packaging system (return status of install)
- added 2 plugins for automatically create symlinks webmail and phpmyadmin on each website (not enabled by default)

- updated the debian installation instructions