Implement operator negation with existence assumption

[thomaskrause]

This implements #186 by splitting the current BinaryOperator trait into two traits (one that can only be used with nested loop joins and one that can be used with index joins) and adding an automatic implementation of the negated variant for each existing binary operator. This can only use the filter_match function, since there is no way to automatically find optimized implementations for the negation. A (slow) nested loop join is enforced instead. Since the current implementation of the negated operators are non-binding (as defined in #186), this is not an issue since in most cases this will be an additional filter function and not be used to generate new right-hand-side matches for a given left-hand-side.

TO-DOs

• Fix issues reported by clippy in the changed files
• run benchmark to ensure no existing query is affected
• add specific test queries for the new operator

[thomaskrause]

bors r+

[bors]

Build succeeded:

• Execute automated tests on OSX
• Execute automated tests on Ubuntu Linux
• Execute automated tests on Windows
• Execute search tests