Schools should share more code

[thatoddmailbox]

There's a lot of code for the schools that is reimplemented several times and could probably be merged:

• Keeping track of the import status
  • Showing the "you need to update" notification when we set that flag
• Enrollment components
  • This is tricky because the schools are somewhat different here, but not really as different as I thought they'd been when first building everything.
• Announcements/holidays
  • Obviously the actual holidays are different, but the code for them is basically the same.
• I think every school has its own implementation of looping over every date in the range requested in GetView. I'm not really sure how to best simplify this though.
• Parsing username and password in Enroll
  • This is minor, but there's definitely some boilerplate with parsing the username and password from the params map. I don't really think there's a great way to simplify this without removing the flexibility of the params (which is useful for schools that need a bit more logic than just username/password).