Built-in blacklist/watchlist

Problem

Many hackathons have blacklist/watchlist for certain problematic hackers. Currently, we have to manually check for these people.

Solution

Have a list of emails and/or names in the admin page that is scanned across all application answers. If it finds a match, show a warning on the admissions page when selecting a decision and also on the users page.

What this looks like:

1. A string list on the Admin page with a list of names and emails
2. Whenever a user applies, have a function cross-check the application with the names and emails on the watchlist.
3. If a match - have an alert on the page saying that they are on the blacklist/watchlist and delete the application.

Details

Show warning when selecting decision in admissions page and on users list. Need to create a new column in settings table.