[ticket/11959] Use plurals for the language strings.

PHPBB3-11959
[ticket/11959] Fix the NOTIFICATION_QUOTE_TRIMMED text.

PHPBB3-11959
[ticket/11959] Use the plurals system for the untrimmed language strings.

PHPBB3-11959
[ticket/11959] List the last user with "and" instead of a comma.

PHPBB3-11959
[ticket/11959] Add samples for the untrimmed strings.

PHPBB3-11959
[ticket/11959] Add function to create a string list.

PHPBB3-11959
[ticket/11959] Simplify how the users are trimmed.

PHPBB3-11959
[ticket/11959] Rename phpbb_gen_string_list() & fix incorrect var name.

PHPBB3-11959
[ticket/11959] Remove use of plurals and make it possible to use Oxford comma.

PHPBB3-11959
[ticket/11959] Add unit tests.

PHPBB3-11959
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12293] Add missing compact() call to phpBB/phpbb/log/log.php events.
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12292] Improve style details page
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/11357] Correcting invalid markup
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/11904] Update explanation for what Allow CDN does
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12035] Correcting the condition
  [ticket/12035] Adding necessary conditions
  [ticket/12035] Adding link to user posts to ACP page
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12289] Add viewtopic template events for posts specific custom notices
Merge branch 'develop-ascraeus' into develop

# By Joas Schilling
# Via Dhruv (1) and Joas Schilling (1)
* develop-ascraeus:
  [ticket/12268] Do not use substr but just compare the character
  [ticket/12268] Rename class file to recursive_dot_prefix_filter_iterator.php
  [ticket/12268] Move class out of extension namespace and rename it
  [ticket/12268] Do not search in folders starting with a dot
  [ticket/12268] Use FilesystemIterator::SKIP_DOTS
  [ticket/12268] Extension finder should not crawl through .git/ of extensions
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12292] Fix syntax error in admin.css
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12297] Delete user_from column on update
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/10174] Rename "Ban usernames" to "Ban users" in ACP