Improve performance in production

Branch to to fix performance stuff on the server:

• Move save/submit buttons to the top of reviews as well
• Add info on maximum file size for submission (50 MB)
• Delay of 1 second when filtering is applied on a list
• Lazy load teacher assignment tabs
• Show an alert when reviews/feeback is being opened
• disable buttons when server is busy making an assigment or saving/deleting answers
• remove getlatest submission route
• Upload files directly to a temporary folder
• Use workers in separate threads for intesive tasks (like review distribution/group import) fixes #307 (closed)