Add nbgrader create assignment extension
Add example notebook to test toolbar
Ignore ipython checkpoints
Rename "autograder" cells to "test" cells
Update toolbar to only have 'solution' and 'grade' cells
Update example notebook
Only color grade cells when toolbar is active
Use booleans for grade and solution, rather than cell_type
Remove check for disable_nbgrader_toolbar
Only add the toolbar to code and markdown cells
Make extension a little more efficient
Don't modify resizable ui css
Use require to get URL for css
Change points text box to number type
Use checkbox ui generator for solution checkbox
Fix styling for points textbox
Remove debug statement
Rename load_ipython_extension to load_extension
Clarify development status of nbgrader
Rename grader_id to grade_id