Convert xml nodes values from str to unicode
PICARD-633: fix up artist's name translations

See http://chatlogs.musicbrainz.org/musicbrainz-devel/2014/2014-09/2014-09-18.html#T20-39-39-835764

Scores help when it comes to ambiguous choices, see tests.
Add dev utility function printable_node()
Merge pull request #359 from zas/PICARD-633

Picard-633: rework aliases selection for translation of artist's name