Changed users API to databank [#272]

Behavioural changes:

* API functions no longer return values, callbacks must be submitted. These will be documented soon.
* resolveUser now returns the user record instead of just a resolved username. This means many less search operations.
* resolveUser now returns false instead of the original nick passed to it in the case of being unable to find a user.
* getServerUsers has been removed, as it is now unnecessary.