allow user to set listen address and port

[dstathis]

Issue

Users need to be able to set the listen address and port of the https server. #54

Solution

Create a config option and forward it to waitress-serve.

Testing Instructions

1. Change the listen address in the config file.
2. Run COS Alerter.
3. Check that it is listening on the correct port.

Release Notes

Users can now set a custom listen address for the http server.

[mmkay]

The PR looks fine, however I'm wondering if it wouldn't be useful to add a test case for testing the newly exposed config property?

[dstathis]

The PR looks fine, however I'm wondering if it wouldn't be useful to add a test case for testing the newly exposed config property?

I considered this but decided the feature is trivial enough.