Dynamically update sports + sportsbook data

[jemorriso]

This PR is meant for commits made on June 16th that were mistakenly merged with
the previous PR. These commits address dynamically adding sports + sportsbook
data depending on user configuration. The idea is that the user can decide when
to update the local sports + sportsbook data instead of making 2 API calls every
time they create an instance of the Rundown class.

cc32e7a

• If the user sets refresh_cached_data to
  True on creating an instance of the Rundown class, the static data will be
  updated
• refresh_sportsbooks and refresh_sports functions added in order to write
  data to local files
  • alternatively, logic for these functions could be added to sports and
    sportsbooks methods

d79f518

• The use_sportsbook_name validator defaults to sportsbook ID if a name is not
  found (if the local sportsbook data hasn't been updated)

1237cce

• static module with build_sportsbook_dict and build_sports_dict created,
  together with sports.yaml and sportsbook.yaml
  • the .yaml files are local copies of the data returned from the server

Todo

• add docstrings