Fix jobunit/change_form translations

jobunit/change_form.html has {% trans "Newsletter Erstellen" %}, but it
should read {% trans "Send Newsletter" %} and allow the translations to
convert it appropriately.
FIx typo in Job help text
add request context for unsubscribe view

Adding the request context to the unsubscribe view allows for a more
versatile unsubscribe template
support Pillow

from PIL import Image works on both PIL and Pillow
add 2 new authors