Implement confirm password field for new users

[phil-davis]

Like in core owncloud/core#29901 where we now have a "retype password" field when a user has been sent an email with a password reset link. (core PR owncloud/core#30981 has the core code)

Do similar for when the administrator creates a new user with just a username and email address. The link in the email should be a page that asks for the password to be typed twice.

[sharidas]

I think where ever we deal with password reset, it should be entered twice. Will bring consistancy to our UI. Totally agree with you.

[phil-davis]

I am doing this straight away, because acceptance tests were trying to drive this "new user" password setting case just the same as the "reset password" case. PR coming in a moment...

[phil-davis]

See PR #146 for implementation.