Add delivery progress

[ramikg]

Overview

This PR adds emoji art depicting the courier's progress towards the destination: Additionally, a "get ready" message is sent 7 minutes before the delivery ETA.

Reasoning behind the new configuration items

• ORDER_DONE_TIMEOUT – Now we actually have to wait for the order to be done (instead of just ready).
• TIME_TILL_GET_READY_MESSAGE – Use another duration instead of the "7 minutes" mentioned above.
• ORDER_DESTINATION_EMOJI – Users will probably want to configure this to be your company's logo.

Additional considerations

• I've decided to edit the rates message instead of adding yet another reply, in order to avoid bothering the tagged users.
• I've (ab)used the existing currentlyWorkingOrders map to save the relevant groupOrder pointer.
• In order to get the ID of the rates message, I've modified informEvent to return the ID of the new reply.
  Which meant I had to modify all calls to said function. I hope this is not an issue.