Add additional warning to ´experimental' notice in setup for stack.
Add a notice the shipped PostgreSQL is deprecated.
Make the external PostgreSQL database the default option.
Make 1.7 the default version (stable_version': '1.7', in docs\conf.py)
Update mergify.yml with 1.8 version
Rate limiting was already redesigned to use Python limits. This
introduced some unexpected behavior, including the fact that only
one criteria is supported per limiter. Docs and setup utility are
updated with this in mind.
Also, the code was made more generic, so limiters can be delivered
for something else than authentication. Authentication-specific
code was moved directly to the authentication routine.
