Halfway fix for devilry#19

Added ng-non-bindable to assignment text in assignments.django.html
which prevents it from being interpreted by AngularJS.
AceMarkdown needs to be fixed as well.
Removed bleach as it was not in use.

trix/trix_core/trix_markdown.py

@@ -1,5 +1,4 @@
 import markdown
-import bleach
 from django.utils.safestring import mark_safe
 
 
@@ -20,4 +19,3 @@ def assignment_markdown(inputmarkdown):
             'markdown.extensions.tables',  # Support tables
         ])
     return mark_safe(md.convert(inputmarkdown))
-    # mark_safe(bleach.clean(md.convert(inputmarkdown), tags=['p']))

trix/trix_student/templates/trix_student/include/assignment.django.html

@@ -31,7 +31,7 @@ <h2 id="assignment-{{ assignment.id }}">
         </div>
     {% endif %}
 
-    <section class="trix-assignmenttext  trix-markdownarticle">
+    <section class="trix-assignmenttext  trix-markdownarticle" ng-non-bindable>
         {% trix_assignment_markdown assignment.text %}
     </section>
     {% if request.user.is_authenticated and not disable_howsolved_box %}