Implemented Transient connector
Updated embedded relations to use transient connector

embedsMany will now use a connector's generated method, when defined.
Also, the id property type is now inferred correctly, making the autoId
option obsolete. However, a new option, forceId, can be set to enforce
the use of auto-generated ids, preventing any explicitly (user-)set id
values.
Merge pull request #268 from fabien/feature/transient-model

Transient connector implementation