adding 'time until' copy into due date UI

apps/openassessment/templates/openassessmentblock/peer/oa_peer_assessment.html

@@ -12,7 +12,12 @@
             <span class="wrapper--copy">
                 <span class="step__label">Assess Peers</span>
                 {% if peer_due %}
-                <span class="step__deadline">due <span class="date">{{ peer_due }}</span></span>
+                <span class="step__deadline">due
+                    <span class="date">
+                        {{ peer_due }}
+                        (in {{ peer_due|timeuntil }})
+                    </span>
+                </span>
                 {% endif %}
             </span>
         </h2>

apps/openassessment/templates/openassessmentblock/self/oa_self_assessment.html

@@ -13,7 +13,12 @@
             <span class="wrapper--copy">
                 <span class="step__label">Assess Yourself</span>
                 {% if self_due %}
-                <span class="step__deadline">due <span class="date">{{ self_due }}</span></span>
+                <span class="step__deadline">due
+                    <span class="date">
+                        {{ self_due }}
+                        (in {{ self_due|timeuntil }})
+                    </span>
+                </span>
                 {% endif %}
             </span>
         </h2>

apps/openassessment/xblock/openassessmentblock.py

@@ -380,25 +380,20 @@ class OpenAssessmentBlock(
         context = Context(context_dict)
         return Response(template.render(context), content_type='application/html', charset='UTF-8')
 
-    def format_date_string(self, date):
-        """Takes a date string, and formats it to be a user facing date.
-
-        Format a date string to be user facing.
-
-        """
-        return dateutil.parser.parse(
-            unicode(date)
-        ).replace(tzinfo=pytz.utc).strftime(DATE_FORMAT)
-
     def format_datetime_string(self, datetime):
         """Takes a datetime string, and formats it to be a user facing time.
 
         Format a datetime string to be user facing.
 
+        Args:
+            datetime (str): A ISO formatted Datetime String, to be converted to
+                a datetime object with UTC timezone.
+
+        Returns:
+            datetime with UTC timezone from the given string.
+
         """
-        return dateutil.parser.parse(
-            unicode(datetime)
-        ).replace(tzinfo=pytz.utc).strftime(DATETIME_FORMAT)
+        return dateutil.parser.parse(unicode(datetime)).replace(tzinfo=pytz.utc)
 
     def add_xml_to_node(self, node):
         """