[ticket/11744] Group join request notification

PHPBB3-11744
[ticket/11744] Move notification from ucp_groups to group_user_add

PHPBB3-11744
[ticket/11744] Create null log class (primarily for unit test)

PHPBB3-11744
[ticket/11744] Create base notification test class for setup

PHPBB3-11744
[ticket/11744] Group request test

PHPBB3-11744
[ticket/11744] Cleanup

PHPBB3-11744
[ticket/11744] Include once

PHPBB3-11744
[ticket/11744] Fix functional test case that's failing

PHPBB3-11744
[ticket/11744] Tables are not truncated in some dbms during tests

PHPBB3-11744
[ticket/11744] Empty notifications tables after testing them

PHPBB3-11744
[ticket/11744] spelling

PHPBB3-11744
[ticket/11744] Fix tests for postgresql

PHPBB3-11744
[ticket/11744] Copyright year

PHPBB3-11744
[ticket/11744] Language

PHPBB3-11744
[ticket/11744] Comments

PHPBB3-11744
[ticket/11745] Group request approved notification

PHPBB3-11745
[ticket/11744] Helper function to assert notifications in base test

This also fixes tests

PHPBB3-11744
Merge branch 'ticket/11744' of github.com:EXreaction/phpbb3 into ticket/11745

* 'ticket/11744' of github.com:EXreaction/phpbb3:
  [ticket/11744] Helper function to assert notifications in base test
[ticket/11745] Add test for group request approved

PHPBB3-11745
[ticket/11373] Prune old read notifications with cron

PHPBB3-11373