before the people cache was never used, because the 'args' parameter in
the 'self._people_cache.get(args)' call was a list/tuple object; but the
people cache dictionary has only strings as keys
-> so there were always database queries for the persons which slowed
down the sync process
also renamed 'args' to 'name', because basically a person gets searched
only by its name (see queries.py)
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