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)
Note: This has a previously applied optimization of using a local cache.
Before:
```
458570 66.934 0.000 66.934 0.000 {method 'execute' of 'sqlite3.Cursor' objects}
246771 58.075 0.000 58.075 0.000 {method 'fetchone' of 'sqlite3.Cursor' objects}
```
After:
```
368883 66.220 0.000 66.220 0.000 {method 'execute' of 'sqlite3.Cursor' objects}
157084 58.160 0.000 58.160 0.000 {method 'fetchone' of 'sqlite3.Cursor' objects}
```
Once again, the number of calls to execute and fetchone are reduced but
the total time spent executing each is relatively stable.
* Added profiling info
* Resort to the expensive database lookup only if the person exists in the
database.
* Prevent any access to the people database unless a person must be added.
* Bulk operations where possible.
* Prepare for a new install and the table not existing.
