Support custom Entity Types via Services Entity

[signalpoint]

Add support for non-core entity types. We should easily handle ECK and code created entity types.

• [x] Create
• [x] Retrieve
• [x] Update
• [x] Delete

[signalpoint]

See the README for usage: https://github.com/signalpoint/jDrupal/tree/7.x-1.x#custom-entity-types

[signalpoint]

Still need support for update and delete.