[FEATURE] Expand sign up to allow double confirmation of email/user id input and supporting text

[davoutuk]

Business problem:
The current sign up form is very neat but doesn't allow for a mistake in the user entering an incorrect email address. And also there is no opportunity to introduce some commentary text to explain how the sign up process works

Improvement:
Add new options to the sign up form, like:

1). double input of user email address? (bool)
If set to TRUE this would display two input fields for the user email address, as 'Email address' and 'Confirm email address'

2). Sign up commentary text
An optional String field that if set to non null would have this text displayed at the top of the sign up form. This text could be used to explain how the sign up works, e.g. use of verification email

3). Optional confirm sign up confirm prompt
An optional boolean sign up form property that is set to true will display a 'are you sure?' style prompt after the user has clicked on the sign-up button. The confirm prompt will display the user account name, allowing the user to choose not to confirm the sign up and go back and change the user name.