Adding settings and requirements for dogslow.

[e0d]

@cpennington @jarv @feanil

@jtauber for the new requirement

The creates a new environment that inherits everything from aws.py and does the following

• prepends the doglow middleware to the inherited list of middleware classes.
• configures dog slow.

This PR does not integrate dogslow directly into aws.py as I'd like to run in selectively for a while before blessing it.

We should also change the logging directory, but that will require an additional PR against the config repo to create a sensible directory and/or integrate dogslow with rsyslog.

[cpennington]

I'd rather have dogslow being an option in aws.py, rather than being a separate environment file. The proliferation of environment files is unfortunate, in my mind.

[e0d]

Seems reasonable, but what scheme do we use for optionally including it? Environment variable?

[cpennington]

It's aws.py, so read it out of env.json. Have a single variable that controls whether it's on or off, and then more variables for the more specific configuration as needed.

[jtauber]

LGPL is fine.

[e0d]

@cpennington I'm going to close this for now. I don't think more JSON config is the way to go, but take your point about the proliferation of settings files.