Gradescope Permissions / Sync Errors Need to bubble up

[cycomachead]

If you sync assignments but have not added gradescope-bot to your Gradescope course, an error will occur, but it will be hidden.

• the flash still seems to show red, so we should be able to access the error message and display it to the user.
• store the error message w/ the rest of the sync info in the db
• display the error message on the assignment sync page

[cycomachead]

I've tried to address some of this. We could do more to explain permissions issues especially.