Portuguese Brasilian Subtitles support

gui/slick/images/flags/pb.png

lib/subliminal/language.py

lib/subliminal/services/addic7ed.py

lib/subliminal/services/opensubtitles.py

lib/subliminal/services/podnapisi.py

lib/subliminal/services/subswiki.py

lib/subliminal/services/subtitulos.py

lib/subliminal/services/thesubdb.py

lib/subliminal/services/tvsubtitles.py