Fix remaining bugs on ManageData page

[matthewcawley02]

List of remaining bugs:

• [x] Add Course and Save Course buttons shouldn't have hover graphics when greyed out
• [ ] Logic for deciding which of those buttons to grey out is one keypress behind
• [x] Only displays the course code for courses in the database, even when there is more information
• [x] When creating/saving course, the change should show up immediately instead of requiring a refresh
• [x] After creating a course, grey out the add course button (until the course code field is changed) so you can't duplicate it
• [x] Bug where if a lecture and tutorial overlap in time but on different days, the system flags it as invalid
• [x] DeleteData and UpdateData requests fail

[matthewcawley02]

@mazfil @RachelCaoCC are there any other small bugs to add here? trying to collate them into one issue, unless they deserve their own