Added request WCA id page, and cleaned up error messages when trying to log in

[jfly]

This is some long overdue polishing with our accounts system.

A lot of people think they already have WCA website accounts because they have a WCA id, or because they used the WCA website to register. Now when you try to log in with an unassigned WCA id, we give a helpful message (#235):

If they follow those instructions and create an account, they will see a notification to request a WCA id:

Clicking that notification will take you to the "request a WCA id" page:

After they choose a WCA id, as per @Luis-J-Ianez's idea, we suggest some likely delegates, but we also give them a search box to pick any delegate:

Note that we don't let them request a WCA id that has already been assigned to a non-dummy user:

But you can request a WCA id that belongs to a dummy account:

After selecting a WCA id and a delegate, the user will see a success! message:

Both the delegate and the user will be emailed:

And the delegate will see a notification every time they log in:

The "approve a WCA id request" piece of of this is the least polished, but I think it works fine. First you click approve:

Which just moves the WCA id from the unconfirmed textbox into the confirmed text box:

The delegate still has to press save after this.

[Luis-J-Ianez]

Looks awesome, Jeremy. Just one comment: to me it sounds weird the "Request WCA id" wording. I know that it's stupid me suggesting that there are issues in your English, :P but requesting something that you already have, is not weird? What about "Claim your WCA id"?