Adds an additional decorator (and refactors the original HTTP decorator)
to handle cloud event structures as in the functions_framework library.

Additionally, removes the decorator library dependency as no longer used
as this was not behaving nicely alongside the functions_framework now
that the function signatures are important.

Finally, set a new location for the 'root' gunicorn configuration file
at /etc/gunicorn.conf.py and updated the Dockerfile to copy that across.