[ticket/13207] Add default subscription options for newly registered users

PHPBB3-13207
[ticket/13207] Move default user notifications settings to user_add()

PHPBB3-13207
[ticket/13207] Add notification manager mock to user_add method in tests

PHPBB3-13207
Merge remote-tracking branch 'github-marc1706/ticket/13207' into prep-release-3.1.0

* github-marc1706/ticket/13207:
  [ticket/13207] Add notification manager mock to user_add method in tests
  [ticket/13207] Move default user notifications settings to user_add()
  [ticket/13207] Add default subscription options for newly registered users
Merge branch 'prep-release-3.1.0' into develop-ascraeus

* prep-release-3.1.0:
  [ticket/13207] Add notification manager mock to user_add method in tests
  [ticket/13207] Move default user notifications settings to user_add()
  [ticket/13207] Add default subscription options for newly registered users
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/13207] Add notification manager mock to user_add method in tests
  [ticket/13207] Move default user notifications settings to user_add()
  [ticket/13207] Add default subscription options for newly registered users
[prep-release-3.1.0] Add 3.1.0 gold release migration
Merge branch 'prep-release-3.1.0' into develop-ascraeus

* prep-release-3.1.0:
  [prep-release-3.1.0] Add 3.1.0 gold release migration
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [prep-release-3.1.0] Add 3.1.0 gold release migration
[prep-release-3.1.0] Add CHANGELOG for 3.1.0
Merge branch 'prep-release-3.1.0' into develop-ascraeus

* prep-release-3.1.0:
  [prep-release-3.1.0] Add CHANGELOG for 3.1.0
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [prep-release-3.1.0] Add CHANGELOG for 3.1.0
[prep-release-3.1.0] Add missing CHANGELOG entries for RC6
Merge branch 'prep-release-3.1.0' into develop-ascraeus

* prep-release-3.1.0:
  [prep-release-3.1.0] Add missing CHANGELOG entries for RC6
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [prep-release-3.1.0] Add missing CHANGELOG entries for RC6
[ticket/13207] Use assert_checkbox_is_checked for registration test

PHPBB3-13207
[ticket/13216] Use gmdate() instead of date() in datetime tests

PHPBB3-13216
[develop-ascraeus] Update version number to 3.1.1-RC1-dev
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [develop-ascraeus] Update version number to 3.1.1-RC1-dev
Merge remote-tracking branch 'github-marc1706/ticket/13207' into develop-ascraeus

* github-marc1706/ticket/13207:
  [ticket/13207] Use assert_checkbox_is_checked for registration test