Until now, only `waitingJoins` was stored separately per network, while
`channels`, `sentGhost` and `identified` had one common value per plugin
instance. Instead of making everything a dictionary indexed by network
name like `waitingJoins`, let's bundle all the state together in a class
and store *its* instances in such a dictionary.
This fixes at least one race condition, for which a test case was added.
Even with `noJoinsUntilIdentified` set, the bot would let joins through
as long as *any* one network has already finished identifying.
I didn't observe any error with the current set of tests but adding
another one that used "services password" caused oen of these tests
to fail. Given that tests shouldn't leave traces in global state,
let's reset the configured passwords in finally blocks.
