(bug 44683) GuidGenerator JavaScript implementation

- patch set 2: Passing prefixed id to claim guid generator as long as the backend does not
deliver a serialized EntityId object along with a serialized Entity.
- patch set 3: rebase
- patch set 4: rebase
- patch set 5: Split claim GUID generator from plain GUID generator addressing comments on
patch set 3.

Change-Id: Ica945337f52110cad9f2febfaf52e695b6e302fe
Merge "(bug 44683) GuidGenerator JavaScript implementation"