(PDB-660) Environments end-point streaming

This patch adds streaming to the environments end-point.

Signed-off-by: Ken Barber <ken@bob.sh>
(PDB-660) Provide better validation for query params on environments & singleton end-points

This does proper validation for environments now, but also stops allowing
pagination and query parameters for end-points that return single items
since neither of those things make sense in that context.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #981 from kbarber/ticket/master/pdb-660-environments-streaming

(PDB-660) Environments end-point streaming