Hide nbgrader css when toolbars are rebuilt/hidden
Add tests for the grade cell css changes
Merge pull request #23 from jhamrick/remove-nbgrader-css

Hide nbgrader css when toolbars are rebuilt/hidden
Fix ordering of celltoolbar elements
Fix tests
Add specific test for tabbing
Fix CSS tests
Merge pull request #22 from jhamrick/fix-tabbing

Fix ordering of celltoolbar elements