fix show VA warning and make some html fields required
The two things here are that if you add new artist fields on the upload/request page, the check for "Various Artists" was only hooked up to the first box. This makes it check all of the artist fields for various artists (and variants) showing the Various Artists message above it if detected.
This also makes a bunch of fields on the upload page required so in most browsers (not Safari), failure to fill it in will not allow you to submit until it has something.
Requested by Mirai
See merge request !17
itismadness