Initial multi-database support.

Since i *really* need it, I built multiple database support today :-)

Currently it does some assumptions:
- We are talking about multiple revisions of the same basic database here.
- These databases are all accessible on the same MySQL username with the same account.

I also made it so that you can have naturally sorted directories with a short description of what the change actually was, so now yo can have your structure like this (if you want)

001 - Create Extras, Create Looplijst
002 - Alter Slides
003 - Create Devices
004 - Alter Backend Extras
005 - Alter extra_looplijst_records
006 - Alter PresentationGroups
007 - Alter Addons
008 - Addons lastcached
009 - Create client_crmconnectors and invoice_transferlog
010 - Alter client_crmconnectors (continueonfailure)
011 - Create Quotes
(and so on)