ADD: query support
ADD: namespaces to Query and thumbnail as well
FIX: use both dirname and filename to generate thumbnail
ADD: alt and title tags on thumbnails
ADD: dropdownlist memory to query engine
FIX: (automatic) deletion of conditions
FIX: queries for all comparison operands (=, !=, IS, NOT IS, LIKE, NOT LIKE)
ADD: query support

TODO: handling of logical operand OR