Workaround for Django bug with pggettext_lazy

pgettext_lazy currently trips in released versions of Django when it's
passed a byte string: https://code.djangoproject.com/ticket/22565

The recent commit d3ddfa5f79c2197d7614c77ee6b96399acbd3918 added a lot
of contextual markers using pgettext, so a few views tripped.

The workaround is easy enough; just ensure all strings passed to
pgettext_lazy are unicode strings.