Add network and auth subclasses.

[Jeff-Meadows]

• Adds LoggingNetwork to allow clients to see what network calls the SDK is making.
• Adds RemoteOAuth2 to allow auth to occur in a different process or machine from the SDK.
• Adds RedisManagedOAuth2 to allow token storage in Redis, to enable multiple processes or machines to share tokens.
• Addresses issue Token Refresh in a Multiple Process Environment #71 with CooperativelyManagedOAuth2Mixin class.

[boxcla]

Verified that @Jeff-Meadows has signed the CLA. Thanks for the pull request!

[Jeff-Meadows]

Obviously this needs tests, but wanted to review the ideas first and see if we should introduce these classes into the SDK.

[Jeff-Meadows]

Whoops. I refactored the base class to make _store_tokens overridable to avoid overriding this, but then forgot to change it.

[landscape-bot]

Code quality remained the same when pulling 2bb05e3 on box:auth into 51a8a47 on box:master.

[landscape-bot]

Repository health decreased by 0.54% when pulling b35881f on auth into 51a8a47 on master.

• 13 new problems were found (including 4 errors and 7 code smells).
• No problems were fixed.

[landscape-bot]

Repository health decreased by 0.53% when pulling 97a7774 on auth into b661d7e on master.

• 13 new problems were found (including 4 errors and 7 code smells).
• No problems were fixed.

[landscape-bot]

Repository health decreased by 0.53% when pulling 3fff540 on auth into b661d7e on master.

• 13 new problems were found (including 4 errors and 7 code smells).
• No problems were fixed.

[jmoldow]

The callable might not be able to retrieve anything (e.g., the cache might not have this user yet). Should we allow the callable to return None, or allow the tuple elements to be None?