Access Token improvements

• AccessToken now carries an ID. It helps creating a Token Pool.
• More Redaction fixes. some object's Redact() funcs were still returning pointers and used children Redact() wrongly.
• Open Messaging Integration's Client field is now public. This allows calling code to reset the client as needed (like with another access token).
• ClientOptions can be passed a context that can carry a Logger (superseded by the Logger field as needed)