Support OAuth Authentication

[jlost]

It would be nice to support authenticating with OAuth2 bearer tokens rather than just JWT.

[jrfernandes]

You can handle the OAuth flow separately and use the generated tokens with this client:

client = ZoomClient(api_key, api_secret)
client.config["token"] = oauth_generated_token

[pjhinton]

See also #272

[prschmid]

As Zoom only supports OAuth authentication now, as of version 1.2.0, the library has been updated accordingly.