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()
PICARD-630: linear_combination_of_weights() raises exception

It happens when the function is called with empty parts list.
Returns 0.0 instead of raising ZeroDivisionError exception
Merge pull request #355 from zas/linear_combination_of_weights

PICARD-630: linear_combination_of_weights() raises ZeroDivisionError
Move UI_LANGUAGES and ALIAS_LOCALES declarations to their own files

In future, those lists will be auto-generated.
Move all const-related files to new const directory
Merge pull request #360 from zas/consts_cleanup

Move all constants related stuff to new const/
Merge pull request #359 from zas/PICARD-633

Picard-633: rework aliases selection for translation of artist's name
Move cover art related files to a "coverart" sub-directory
PEP8 fixes
Add picard.const to setup.py
Auto-generate list of "packages"

When moving code around, creating new subdirs, one had to add/modify packages list
in setup.py.
So, basically, this patch is just generating an up-to-date list on runtime, including
all subdirs under picard/ and converting them to modules-like names (replace path separator by a dot).
Merge pull request #363 from zas/setup_packages_fix

Auto-generate list of "packages"
Merge pull request #362 from zas/coverart_mv

Re-organize cover art-related files
Resync .po and .pot files