Enhancements for receiving/displaying inter-BBS instant messages (telegrams):

- Fix apparent bug when there was no incoming data.
- Include the sender's avatar if one is found and the sender did not send
  the most recent message to the recipient (don't repeat the avatar
  needlessly).
- Store the information (name, address, etc.) for received imsg's in the
  recipient's property (.ini) file. This makes quickly replying easier.

Note: the receiving messages for a node-number feature should probably just
be removed.