Add SHOW_PROGRESS_SUCCESS_BUTTON feature

Show a button at the top of lms/templates/courseware/progress.html if the
lowest nonzero grade cutoff has been reached. Introduce two settings:
PROGRESS_SUCCESS_BUTTON_URL is the href of that button (the course id is
appended); PROGRESS_SUCCESS_BUTTON_TEXT is the text, defaults to
"Download your certificate"

lms/envs/common.py

@@ -243,6 +243,10 @@ FEATURES = {
 
     # Turn off Advanced Security by default
     'ADVANCED_SECURITY': False,
+
+    # Show a "Download your certificate" on the Progress page if the lowest
+    # nonzero grade cutoff is met
+    'SHOW_PROGRESS_SUCCESS_BUTTON': False,
 }
 
 # Used for A/B testing
@@ -1283,6 +1287,11 @@ GRADES_DOWNLOAD = {
     'ROOT_PATH': '/tmp/edx-s3/grades',
 }
 
+######################## PROGRESS SUCCESS BUTTON ##############################
+# The course id will be appended to the following url
+PROGRESS_SUCCESS_BUTTON_URL = 'http://<domain>/<path>/'
+PROGRESS_SUCCESS_BUTTON_TEXT = "Download your certificate"
+
 #### PASSWORD POLICY SETTINGS #####
 
 PASSWORD_MIN_LENGTH = None

lms/static/sass/course/_profile.scss

@@ -148,6 +148,24 @@
       }
     }
 
+    #course-success {
+      margin-bottom: 30px;
+      text-align: center;
+      > a {
+        @include button(simple, $button-color);
+        @include box-sizing(border-box);
+        border-radius: 3px;
+        font: normal 15px/1.6rem $sans-serif;
+        letter-spacing: 0;
+        padding: 5px 18px 6px;
+        text-align: center;
+
+        &:hover, &:focus {
+          text-decoration: none;
+        }
+      }
+    }
+
     #grade-detail-graph {
       min-height: 400px;
       width: 100%;

lms/templates/courseware/progress.html

@@ -48,6 +48,20 @@ from django.conf import settings
         <h1>${_("Course Progress for Student '{username}' ({email})").format(username=student.username, email=student.email)}</h1>
       </header>
 
+      %if settings.FEATURES['SHOW_PROGRESS_SUCCESS_BUTTON']:
+        <%
+          nonzero_cutoffs = [cutoff for cutoff in course.grade_cutoffs.values() if cutoff > 0]
+          success_cutoff = min(nonzero_cutoffs) if nonzero_cutoffs else None
+        %>
+        %if success_cutoff and grade_summary['percent'] > success_cutoff:
+          <div id="course-success">
+            <a href="${settings.PROGRESS_SUCCESS_BUTTON_URL}${course.id}">
+              ${settings.PROGRESS_SUCCESS_BUTTON_TEXT}
+            </a>
+          </div>
+        %endif
+      %endif
+
       %if not course.disable_progress_graph:
         <div id="grade-detail-graph" aria-hidden="true"></div>
       %endif