Ingres database support

[beno]

I just noticed that there are no mentioning of Ingres at the MetaModel database compliancy page. I think it would be good to try this database out and hopefully verify that it works with MetaModel and DataCleaner.

[kasper]

I tried it out the other day (actually at the Ingres facilities in London, thanks Ingres). It worked fine, so we just need to set up an integration test and make a document for the DataCleanerFeatures page...