[ticket/12701] Add events to user_add function

Add two new events to user_add function
in ./includes/functions_user.php.

core.user_add_before - allow modification of
submitted to function data.
Returns:
@var array $user_row - user_row array - User array
@var array $cp_data - cp_data array - CPF array

core.user_add_after - return user_id, user_row and
cp_data after user registration
Returns:
@var int $user_id - user_id of the new user
@var array $user_row - user_row array - User array
@var array $cp_data - cp_data array - CPF array

Justification:
Allow extensions to parse data before and after
creation of the user.

PHPBB3-12701
[ticket/12701] Rmove before event and expand modify_data

Removing core.user_add_before
Adding $user_row and $cp_data to core.user_add_modify_data

PHPBB3-12701
[ticket/12701] Add change

Change back to since
Add change

PHPBB3-12701
Merge pull request #2586 from lucifer4o/ticket/12701

[Ticket/12701] Add events to user_add function

* lucifer4o/ticket/12701:
  [ticket/12701] Add change
  [ticket/12701] Rmove before event and expand modify_data
  [ticket/12701] Add events to user_add function