fix(templates) Fix userPassword handling in templates

When hash is set but not the password value (which is the default if you
 leave the template fields empty), applying the template to a user would
 result in changing its password, even if he already uses the same hash
 method.
With this change it will leave its password alone if it already uses the
 method, and if the method changed it should complain and ask for a new
 password.
This should avoid users erasing passwords by mistake.

issue #6035