NotInRelationshipRule, removing NotIsNull from DefaultIsNullRule

- Added a NotInRelationshipToken, the NotInRelationshipRule,  and the
NotInRelationshipLoweringRule.

- Attributes now have a "isDefinite" type. We should look into how to
determine this for whether to use "the" vs "a/an".

- Added an issue (10) which shows "IS NOT NULL" becoming a NotNode with
a IsNull child.

- Took out IsNotNull from the DefaultIsNullRule. We should look to
create a DefaultIsNotNullRule that catches IsNotNullNodes and
NotNode->IsNullNode instances.
DefaultIsNullRule now doesn't catch IsNotNull