Signup form bug fix. Deploying to production today

# Why?

 * While doing a deploy to staging and looking around, I noticed a bug that would tell new users "Password (leave this blank if you don't want to change it)".

# What Changed? What's new?

 * Fixed the form to render appropriate messages based on wether its a new or existing user
 * Deploying to production shortly

# What's Next?

 * Help Simon with the new guides PR.