[1.3 Users] Updated Api_registration for sendpass

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | -
| Fixed tickets | -
| Refs tickets  | -
| License       | MIT
| Doc PR        | -

When another module wants to use the Users_registration Api and the registerNewUser method you cannot use the sendpass functionality. When a webshop (e.g. zwebstore) with automatic account creation based on user data with a generated password wants to send the generated password to the new account then this update is needed. Otherwise you cannot send the password. 

Automatic account creation saves 1 extra step in customer approach in webshops. And 1 extra step can be one too many in these fast times.
Merge pull request #1669 from espaan/patch-4

[1.3 Users] Updated Api_registration for sendpass