smb: refactor auth and context logic out of slave
in an effort to implement kdirnotify for smb I needed to revisit the ancient monolithic code structure :| authentication is now in an authenticator class the authenticator class is plugged into a context class and the context takes care of context initialization (and callback handling because the smbc API is a bit meh vis a vis callback context void*). since the authentication now doesn't live in the slavebase anymore the interaction with `checkCachedAuthentication()` was moved into a pure virtual interface class. slavebase has an implementation of that interface and so will the future kdirnotify thingy.
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