[ticket/11842] Use group_id 0 and correct avatar name after creating group

It seems like the function group_correct_avatar() was forgotten while adding
the new avatar system. We now pass the group_id 0 to the upload avatar and
let the function group_correct_avatar() fix the avatar filename after creating
the group like it was done previously.

PHPBB3-11842
[ticket/11842] Replace outdated occurences of user and group avatar_type

user_avatar_type und group_avatar_type are now a string and should therefore
be treated accordingly.

PHPBB3-11842
[ticket/11842] Add migration file for updating avatar type in database

PHPBB3-11842
[ticket/11842] Use only new avatar type in user_delete function

PHPBB3-11842
[ticket/11842] Add missing prefix for group id in avatar data

PHPBB3-11842
[ticket/11842] Use type map for updating avatar types in database

PHPBB3-11842
Merge branch 'develop' of https://github.com/phpbb/phpbb3 into ticket/11842

Conflicts:
	phpBB/includes/acp/acp_groups.php
[ticket/11842] Use avatar_data for obtaining driver that should be deleted

PHPBB3-11842
[ticket/11842] Add functional test for creating group

PHPBB3-11842
Merge remote-tracking branch 'Marc/ticket/11842' into develop

* Marc/ticket/11842:
  [ticket/11842] Add functional test for creating group
  [ticket/11842] Use avatar_data for obtaining driver that should be deleted
  [ticket/11842] Use type map for updating avatar types in database
  [ticket/11842] Add missing prefix for group id in avatar data
  [ticket/11842] Use only new avatar type in user_delete function
  [ticket/11842] Add migration file for updating avatar type in database
  [ticket/11842] Replace outdated occurences of user and group avatar_type
  [ticket/11842] Use group_id 0 and correct avatar name after creating group