no more bots

Removes bots from the x/84 codebase, instead relying on sessionless DBProxy instances.
Not so sure that this is OK.

1. during message polling, the BBS will not do any telnet/ssh I/O, all user screens would be locked.
2. remove int() wrapper, every saved byte code amounts to performance on something like raspberry-pi in this loop
3. remove import statement from if statement for same reason
4. the "main" method should instead be the "run" method of a threading.Thread sub-class
5. The thread runs, contains a time.sleep() in a while loop of poll_interval. No need to do poll_interval, or check-if-already-running, etc.
6. This is launched outside of the engine _loop.
7. Should contain a general exception handler, logs exception as error, but thread keeps on trucking next poll_interval.