More Matcher Improvements

[edwardneo]

Matcher could use some small quality of life updates:

• When slots are submitted, there is a verification modal that lists all of the slots that are being submitted before submission. This was used to indicate linked slots before, but in the future could be updated to have more information, such as the descriptions.
• If slots are created but the form isn't open yet, mentors can see the slots but can't submit their preferences. When they try to submit, there is no indication that the issue is the form isn't open, and if they click off their preferences go away. It would be good to have an indicator or not allow them to change their preferences until the form is open.
• The number of sections per slot can only be updated after preferences are gathered. It may be good to be able to update that before then.
  There are likely more small updates, but these are the ones I could find for now -- no actual bugs. These are all pretty minor and straightforward to implement, mainly on the frontend side.