Normalize country names more aggressively for ISO code lookup

Summary:
Without increasing the number of ambiguities this makes the country
detection a bit more robust and shrinks the database by about 50kB/10%.

While stripping non-letters and diacritic marks in Latin is fairly
straightforward and predictable, the results were less helpful in e.g.
Hangul, therefore the fairly fine-grained approach.

Reviewers: mlaurent

Reviewed By: mlaurent

Subscribers: mlaurent, kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D20479