Move deps to requirements.txt

I'm told that this is a more normal way to do it. Just picking version numbers based on what I already have installed... since I know it works with that. python-dateutil forced to version 2.2 because that's the version expected by the monkeypatch hack in googlecalendar.py.
utils.spammable: Prevent a command from being spammed by idiots.
remove !wiki
revert !explain to mod-only
remove !#d#
utils.spammable: multiplicative increase/additive decrease algorithm for determining timeouts
utils.spammable: faster decay