Webhooks don't support the threading yet, so this is token only.
In discord you can reply on each message of a thread, but this is not possible in mattermost (so some changes added there to make sure we always answer on the rootID of the thread).
Also needs some more testing with slack.
update : It now also uses the token when replying to a thread (even if webhooks are enabled), until webhooks have support for threads.
