Add more excluded keys from storage

[Tim Kinnane]

Only the bot instance is removed from states and other objects before keeping
via storage adapter. This improves performance and prevents crashing when store
encounters cyclical references in data. Could probably find some more attributes
that aren't required in storage, to reduce memory requirements.

see https://github.com/Amazebot/bbot/blob/master/src/lib/brain.ts#L11