disable grading saving button after submit to prevent duplicate requests
refine achievement tests code
add a test case for destroy action
Merge pull request #273 from wangqiang1208/test/hackathon-tests

re-write announcement test cases( refine coding style )
Merge pull request #274 from wangqiang1208/bugfixing/gradings-saving-double-clicking-duplicate-requests

disable grading saving button after click submit to prevent duplicate requests