Entity changes/Schema rename

To prevent confusion and start a better naming convention for Quiz and Question entities, rather than nodes, all node-related tables are renamed to exclude the "node" bit. Schema fields are also renamed to remove any mention of "nid".

Note that this will affect any custom queries and Views that are using these tables. If solely using Entity API, or EFQ, those queries will not be affected, as when Entitie were introduced in 7.x-5.x they were preemptively named based on proposed naming of the tables (e.g. quiz_result => quiz_node_results table). Additional relationships may have to be added to Views to pull in Quiz entity data that was previously available as part of the node.

Additionally the "Quiz" content is being migrated away from the "Quiz" content type into an entity type.

The "Question" content types are being completely migrated to a "Question" entity type, with question bundles.
Fields and data will come along.

The original "Quiz" content type will remain. However a new entity reference field will be added to Quiz, and be related to the migrated Quiz entity type. This way we do not completely break any custom fields or displays that have been added to the content type. The tabs and take quiz button will remain.