Cannot add seed URLs without the protocol

[ayberk]

If you try to add URLs without the protocol (http://site.com vs site.com) while creating a new crawl, only the file selector part is highlighted as wrong. It makes it kind of hard to realize what's wrong.

[brittainhard]

I'm going to integrate a feature into the next PR that will show which URLs have errors. This works on the edit seeds page but not on the add seeds page.

[ahmadia]

Maybe we should also have a note explaining that the protocol is required for seeds lists?