[ticket/11600] Increase code test coverage of avatar manager

Currently, not all methods and their possible behaviors are tested with unit tests.
Add them for better code coverage.

PHPBB3-11600
[ŧicket/11600] Split get driver tests into tests for all and only enabled ones

PHPBB3-11600
[ticket/11600] Use local variable for $user in test_localize_errors

PHPBB3-11600
[ticket/11600] Use lowercase null and remove duplicate test cases

PHPBB3-11600
Merge branch 'develop' of https://github.com/phpbb/phpbb3 into ticket/11600
[ticket/11600] Remove duplicate test case

PHPBB3-11600
[ticket/11563] Fix subPanels()

Fix subPanels() code
Modernize subPanels() with jQuery
Use HTML5 data attributes instead of including JS

PHPBB3-11563
[ticket/11563] Remove unused JS variables

Remove unused JS variables from posting_buttons

PHPBB3-11563
[ticket/11563] Dynamically generate panels list

PHPBB3-11563
[ticket/11563] Remove duplicate code

PHPBB3-11563
[ticket/11553] Move bulletin points to pseudo class

Move bulletin points for .linklist lists to pseudo class
Group pseudo classes for .linklist.bulletin and .icon-notification

PHPBB3-11553
[ticket/11553] Replace bullet with unicode

PHPBB3-11553
[ticket/11553] Typo

PHPBB3-11553
[ticket/11112] Use https for user-visible links to phpbb.com

PHPBB3-11112
[ticket/11112] Do not change opensource.org link to https

PHPBB3-11112
[ticket/11684] Remove useless confirmation page after login and admin login

PHPBB3-11684
[ticket/11685] Remove logout confirmation page

PHPBB3-11685
[ticket/11674] Do not include vendor folder if there are no dependencies.

PHPBB3-11674
[ticket/11670] Consistency with logo: Replace "phpBB(tm)" with "phpBB(R)".

PHPBB3-11670
[ticket/11686] Not checking for phpBB Debug errors on functional tests

PHPBB3-11686