Quoting tables + use of sqlite

Some changes made to KeenActiveDataProvider to quote the column names for the 'GROUP' - it blocked for proper use in Postgresql.
Also added sqlite database for easier demonstration - however, use case 2 does not work there.

Further changes would be needed for Postgresql (see (demo of) www.yiiframework.com/extension/relatedsearchbehavior/ ).
Also added 'extrakeys' member - this serves in some cases (but I've added that a while ago and must look why exactly).