XMPP with Metronome

As said in howtoforge forum, here is my merge request for XMPP management with Metronome XMPP server. This is my first modification of ISPConfig, so please do a review of my code. Especially the Usage of client limits.

I created a snippet with the required command to install metronome on a debian based system. Please also have a look on my changes in installer. I am only famillar with debian based systems so it might need some changes e.g. to add the init script to runlevels. http://git.ispconfig.org/Quest/ispconfig3/snippets/1