One Relationship Handler to Rule Them All. (Props to solotandem for the wild idea.) Compare the Views subdir to 5a91a18e.

Provide the scaffolding necessary to get endpoint->relation table->endpoint views relationship handlers.

Revert to Views implementation #1 but using a proper relationship handler. TODO: convert relation table joins to proper handlers, too.

Views integration: setup relation: type as filter_in_operator instead of string #1365406 by dereine.

Replace relationship definitions to cover all the bases and so Relation plays well with Views. #1361780 by solotandem, dereine and chx. Needs followups

Moved the whole Views options thing to the right class, dereine patched Views for us and I made sure the query, no matter how complicated is well indexed.

Partial rollback of commit by naught101: change name back to label, except on relation_type editing form.

Views fixes: directional support needs to be reimplemented, this one is broken, commented out for now. We were not restricting to the relation_type in the JOIN. Finally, the JOIN was always inner, now it's whatever it needs to be.

Issue #1165286 by naught101: Changed Label->Name everywhere, fixes machine_name. Also fix some coding inconsistencies.

Issue #1163876 by naught101: Fixed Relation Add form does not pick up bundles described in hook_entity_info_alter().

Views integration now uses field SQL storage too. Let's try to write the ugliest query with the fewest clicks in Views!