working drop pdf/image
Add messages for new teachers to help create worksheets
Merge pull request #76 from andrewjadams3/new-teacher

Add messages for new teachers to help create worksheets
fixing what I broke
Merge pull request #75 from andrewjadams3/drag/drop

Drag/drop
Todo list refreshes after student submits response
Implemented auto-selecting class codes; File dropbox can be clicked to bring up file upload dialog
File upload will work if the same file is reselected after an error