Ratelimit plugin can send messages out of order

[ChrisD]

If ratelimit pluging starts limiting messages to a user it is possible that the user might end up received the messages from EnDroid in a different order to what they were sent in.

Once the ratelimit hits messages are added to a queue and a timer started to drain the queue.
If a messages is sent out of endroid before the timer fires but after a new token is made available the most recent message will be sent before the queued ones.

Fix is to have sc.accept to return the msg to send (or None if know message should be sent).
This msg will either be the message on the fron of the queue if there are messages on it, or the message being filtered if there are no messages on the queue.