[ticket/12822] Remove "None" option from avatar select boxes

This option is just used for deleting avatars for which we already have
a checkbox.

PHPBB3-12822
[ticket/12822] Add method for deleting avatars and use confirm_box

The method will take care of the actual deletion process in the avatar manager.
Additionally, we'll be using a confirm box while deleting the avatar to prevent
users from accidentally deleting their avatars.

PHPBB3-12822
[ticket/11854] Move captcha stuff to phpbb/ and use DI for plugins

PHPBB3-11854
[ticket/11854] Add a migration to update the captcha_plugin setting

PHPBB3-11854
[ticket/11854] Add missing dot in the migration file

PHPBB3-11854
[ticket/11854] Fix migration

PHPBB3-11854
[ticket/11854] Migrate all old php4 constructor

PHPBB3-11854
[ticket/11854] Split phpbb\captcha\gd.php

PHPBB3-11854
[ticket/11854] Fix various comments

PHPBB3-11854
[ticket/11854] Rename captchas.factory service to captcha.factory

PHPBB3-11854
[ticket/11854] Fix coding style

PHPBB3-11854
[ticket/11854] Remove constants and use DI for QA tables

PHPBB3-11854
[ticket/11854] Remove unused globals

PHPBB3-11854
[ticket/11854] Fix the factory in \phpbb\auth\provider\db

PHPBB3-11854
[ticket/11854] Base the migration on rc2

PHPBB3-11854
[ticket/11854] Fix comments

PHPBB3-11854
[ticket/11854] Change the error message in reCaptcha

PHPBB3-11854
[ticket/11854] Use a set_name method instead of overriding get_service_name

PHPBB3-11854
[ticket/11854] Don't override get service name in nogd

PHPBB3-11854
Merge remote-tracking branch 'github-marc1706/ticket/12822' into develop-ascraeus

* github-marc1706/ticket/12822:
  [ticket/12822] Fix test runs of avatar manager_test
  [ticket/12822] Add method for deleting avatars and use confirm_box
  [ticket/12822] Remove "None" option from avatar select boxes