Convert course home page to Bootstrap

LEARNER-1694

Fix a11y failure

Fix header styling

Fix layout issues

Further layout fixes

lms/djangoapps/courseware/testutils.py

@@ -32,7 +32,7 @@ class RenderXBlockTestMixin(object):
         '<ol class="tabs course-tabs"',
         '<footer id="footer-openedx"',
         '<div class="window-wrap"',
-        '<div class="preview-menu"',
+        '<div class="preview-menu container"',
         '<div class="container"',
     ]