Improved detection of housenumber letters and housenumber additions

[vmenger]

The logic for detecting housenumber letters (1a) and housenumber additions (1-bis) is not very complete, and Deduce thus not always correctly annotates the information following the housenumber. There seem to be no strict rules on what can follow a housenumber. Currently Deduce only detects a single letter (case insensitive) after a housenumber, optionally separated by a whitespace (so 1a, 1A, 1 a and 1 A). The information is usually not very privacy-sensitive, so not very high priority, but would still be nice to do it a bit cleaner.