[#1725] Filters received shouldn't be modified

This means that if the user sends us:

    'filters': { 'age_between': [20, 30] }

We should return that unmodified in the query result, even though internally
that might be translated to something else or removed.
[#1725] Guarantee that tests fail for the correct reason
[#1725] Add test to guarantee that every field in datastore_search is valid