More improvements to the Python search algorithm

[lonvia]

Timing real-life search request uncovered some more inefficiencies in the query builder for search requests:

• when searching for housenumbers as a name, there is no need to look up attached housenumbers
• drop more searches that look to be searching for stop words only
• block exceedingly long searches (they are more likely user input error and never yield usable results)
• disallow a postcode in the first position when doing a classic address search

With these changes the geocoder-tester test suite now is performance-wise at par with the PHP implementation while finding more correct results.