Optimization of distinct() and or()

Calling key.toString() instead of doing JSON.stringify(). The reason is:
IndexedDB keys can only be
* Strings: JSON.stringify() ok. toString(): better.
* Numbers: JSON.stringify() ok. toString(): better.
* Dates: JSON.stringify() ok. toString(): ok (localization doesnt matter
since it is used temporary)
* Arrays: JSON.stringify() ok. toString(): better (will do [].join(','))