12-Handle configurable constants

The only repeatedly used constant that hasn't been configured (other than the path to the config file) is the allowed probabilities. This MR adds allowed probabilities to the config file, as creating a constants.py as suggested in #12 (closed) probably doesn't make sense for one constant. This also adds allowed_probabilities as an attribute to be reused.

I believe #13 (closed) is out of date and should also be closed as probability values are checked in the Config class and no longer checked in the cli commands.

closes #12 (closed) closes #13 (closed)