refactoring jukebox
Merge branch 'dev' of https://github.com/Pierre-Sassoulas/possum into dev

Conflicts:
	locale/en/LC_MESSAGES/django.mo
	locale/en/LC_MESSAGES/django.po
	locale/fr/LC_MESSAGES/django.mo
	locale/fr/LC_MESSAGES/django.po
	locale/ru/LC_MESSAGES/django.mo
	locale/ru/LC_MESSAGES/django.po
	possum/jukebox/forms.py