Problem comp release

[BrandonLMorris]

Problems can now be associated with a competition and hidden from users until that competition begins.

Changes

• Getting one problem will check if that problem's comp_release has started. This adds an extra database query.
• Getting all problems adds a database query to the competitions table, but only one. Start times are stored and checked in memory to minimize performance hit.
• On the front-end, creating/editing a problem has a new competition release field with a dropdown of all upcoming competitions. If selected and saved, the problem is inaccessible to all users (admins can still view by going to the edit route)
  • Note: that this means that previously unhidden problems can be made hidden by associating them with a new competition
  • Note: adding a problem to a competition does not automatically hide it

This feature also includes unit tests. Because that should be a thing.

[BrandonLMorris]

That should have all the fixes. I went ahead and made it so that admins can see the unreleased problems. Without it, there wasn't any real way to add them to competitions (I'm not exactly sure what I was thinking).

[WilliamHester]

Alright, so hiding is working now, but I have one issue. If I create a problem and add it to the competition from the create-a-problem interface, it doesn't actually add it to the competition. If this is intended, then that's alright. Other than that, it seems to be working, so I'm good with merging it.

[BrandonLMorris]

That's not a bug, it's a feature

It's a known limitation. I can add it here or in another PR. Your call.

[WilliamHester]

I'm fine with leaving that functionality right now, because it says "Release with competition," not implying that it will be added to the competition.

If people complain, we can add that in the future.