Address PR comments:

- scripts -> foreman
- drop runHydra
- drop devShell
- move postgresql to buildInputs

Procfile

@@ -1,4 +1,4 @@
-hydra-server: ./scripts/start-hydra.sh
-hydra-queue-runner: ./scripts/start-queue-runner.sh
-hydra-evaluator: ./scripts/start-evaluator.sh
-postgres: ./scripts/start-postgres.sh
+hydra-server: ./foreman/start-hydra.sh
+hydra-queue-runner: ./foreman/start-queue-runner.sh
+hydra-evaluator: ./foreman/start-evaluator.sh
+postgres: ./foreman/start-postgres.sh