Make the SHOW_PROGRESS_SUCCESS_BUTTON feature more flexible

The button text default is now in the template and i18n-able, a
PROGRESS_SUCCESS_BUTTON_TEXT_OVERRIDE option is offered in settings.
The button url now uses string formatting.

lms/envs/common.py

@@ -1288,9 +1288,9 @@ GRADES_DOWNLOAD = {
 }
 
 ######################## 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"
+# The following fields are available in the URL: {course_id} {student_id}
+PROGRESS_SUCCESS_BUTTON_URL = 'http://<domain>/<path>/{course_id}'
+PROGRESS_SUCCESS_BUTTON_TEXT_OVERRIDE = None
 
 #### PASSWORD POLICY SETTINGS #####
 

lms/templates/courseware/progress.html

@@ -48,15 +48,17 @@ 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']:
+      %if settings.FEATURES.get("SHOW_PROGRESS_SUCCESS_BUTTON"):
         <%
+          SUCCESS_BUTTON_URL = settings.PROGRESS_SUCCESS_BUTTON_URL.format(
+            course_id=course.id, student_id=student.id)
           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}">
-              ${settings.PROGRESS_SUCCESS_BUTTON_TEXT}
+            <a href="${SUCCESS_BUTTON_URL}">
+              ${settings.PROGRESS_SUCCESS_BUTTON_TEXT_OVERRIDE or _("Download your certificate")}
             </a>
           </div>
         %endif