Fbmessenger

- Add missing tag parameter to BaseMessenger::send
- Remove invalid message tag

- Adding 2 quick replies content_type: userphone_number, user_mail

- Add share_contents support for share button

- The caller may now pass their own `requests.Session` object to
`MessengerClient`. This is useful for eg. configuring retry behaviour.
- Every method that causes network access now accepts a `timeout`
parameter.

- Add support for `notification_type` in the Send API.

- Breaking API change - `messaging_type` is now required when sending
a message.