Remove not used imports in models. Fix missing spaces in models when operator not preceded by a space. Add missing ugettext_lazy import to Proposal model.
Patch by: Pawel Solyga
Review by: to-be-reviewed
Change Sponsor delete url from /site/sponsor/profile/<link_name>/delete to /site/sponsor/profile/delete/<link_name> to match convention used in Document delete url.
Patch by: Pawel Solyga
Review by: to-be-reviewed