bridge: allow replying to messages not in the bridge's history #59
Description
Using the history for a reply allows implementations with first-class reply support (like Telegram) to get a first-class reply. For other implementations, it provides no benefit. We should support replying to messages that aren't in the bridge's history. To do this, clients with first-class reply support should be able to degrade gracefully to a second-class reply.
I recommend that we implement this after #46. After #46, Message can have ReplyTo *MessageID and ReplyToText *string. If none are set, it's not a reply. Otherwise, if ReplyTo is set then it's a first class Reply. Otherwise otherwise, ReplyToText will have the reply text for a second class reply.