Add queries for worst/best completeness result

I have implemented queries to find the record with the worst,
respectively best completeness metric result. In the next step
I will visualize both.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Implement helper method to return properties hash

For displaying an associative array (hash) with a table I need a list of
all properties in the schema. For the nested structure this should be an
array with either string for flat properties or a hash mapping again to
new arrays of strings or hashes.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>