Support the Jaikoz 'artists' tag, with help from @night199uk and @zas
Merge branch 'master' of github.com:musicbrainz/picard into artists-tag
Merge branch 'master' of github.com:musicbrainz/picard into artists-tag
Merge branch 'master' of github.com:musicbrainz/picard into artists-tag
Update NEWS.txt
Merge branch 'master' into artists-tag

Conflicts:
	NEWS.txt
Merge pull request #188 from mwiencek/artists-tag

Support the Jaikoz 'artists' tag, which stores individual artist names
Set up Transifex to pull the country name translations.
Build picard-countries.po for enabled languages.
Add note to NEWS.txt about PICARD-205 being fixed.
Add a update_countries command to setup.py

It retrieves countries.pot from transifex and uses it to generated picard/countries.py
Add po/countries/countries.pot to git ignore list

We don't want this one to be committed to git repo, it is not created
by parsing Picard code.
Add generated picard/countries.py
Replace the release countries in const.py with import from countries.py.
Use ungettext_countries() for translating country names.
Add po/countries/*.po from transifex
Build, install and use all available locales

Drop the use of UI_LANGUAGES in setup.py which was restricting available translations,
even though translation was available from transifex.

Locales not in UI_LANGUAGES cannot be selected from Picard Advanced UI option,
but will be used if it is set to system default.
Add command get_po_files to setup.py

It runs tx pull with needed options.
Translations with less than 5% translated are ignored.
Use a constant for common options of tx pull