Adding settings and requirements for dogslow.

@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.