Add bleach library to clean notification HTML

lib/bleach/callbacks.py

@@ -0,0 +1,20 @@
+"""A set of basic callbacks for bleach.linkify."""
+from __future__ import unicode_literals
+
+
+def nofollow(attrs, new=False):
+    if attrs['href'].startswith('mailto:'):
+        return attrs
+    rel = [x for x in attrs.get('rel', '').split(' ') if x]
+    if 'nofollow' not in [x.lower() for x in rel]:
+        rel.append('nofollow')
+    attrs['rel'] = ' '.join(rel)
+
+    return attrs
+
+
+def target_blank(attrs, new=False):
+    if attrs['href'].startswith('mailto:'):
+        return attrs
+    attrs['target'] = '_blank'
+    return attrs