PEP8 cleanup, remove unused imports, fix permission check when removing metadata from a document

mayan/apps/sources/widgets.py

@@ -1,6 +1,5 @@
 from __future__ import unicode_literals
 
-from django.conf import settings
 from django.contrib.staticfiles.templatetags.staticfiles import static
 from django.core.urlresolvers import reverse
 from django.utils.html import strip_tags