Allow Users to Recover Lost Logins

[winsmith]

If a user has an email address set – which we don't validate for now btw – then allow the user to enter their username. This will send them an email with a recovery link where they can set a new password.

• Requires The Sending of the Emails #97
• Create new model, PasswordChangeRequest in user_management, with a uuid that needs to be in the URL, a foreign key to the user, and an expiry time of, say 2 hours.
• Create new Template, Form, and View to change the password if the PasswordChangeRequest link is valid
• Create an Email template that lays out the process and has a password recovery link
• if a user requests a password change, send them an email to the specified email address to begin the process
• send an email once the password is changed as an additional security measure