[ticket/11581] Add test to check UCP_PM is enabled/disabled correctly

PHPBB3-11581
[ticket/11581] Enabled private messages after tests

PHPBB3-11581
[ticket/11581] Fix year in copyright header

PHPBB3-11581
[ticket/11581] Hide categories when they have no visible children

PHPBB3-11581
[ticket/11581] Add assertNotContainsLang() for functional test cases

PHPBB3-11581
Merge pull request #2109 from nickvergessen/ticket/11581

[ticket/11581] Hide categories on level 0 when they have no visible children