We were using jamesmtc/madi-gcp-emulator, which appears to be a 3rd
party re-tagged copy of oittaa/gcp-storage-emulator. (The jamesmtc image
contains a Python project that installs the python gcp-storage-emulator
package, which is https://github.com/oittaa/gcp-storage-emulator.)

Long-running functions can now run @cloud_event_handler handlers, and
handlers based on it, like @message_handler.

High-level handlers MR5: Integrate with `ucam_faas` top-level module

See merge request !53