Feature: Signup Form Additions

[cassfantastic]

Disambiguate the signup form by changing from:
*Name
*URL
To:
*Pet Name
*Account Name
And have next to/below the account name, live-updating text showing their URL -
please.pet/[thingthey'vetypedin], as well as whether it's valid or not

Possibly also add (this needs to be unique) or standard phrasing to that effect to the Account Name.