Optimize grading ui optimize ajax

This one is fast. All time consuming queries are moved to Ajax.

Didn't test with a large dataset, but I found in the Pipeline job #28333 for py3.5 and #28332 for py2.7, the 55 tests passed in 17.74s and 19.67s, as compared to 37s and 40s for the latest commit in !27 . The stripped comments seems to be wrong for another push.