[ticket/12268] Extension finder should not crawl through .git/ of extensions

This new filter ignores .svn and .git directories.
When searching for php classes and template files of extensions
we don't need to look inside these directories.

PHPBB3-12268
[ticket/12268] Use FilesystemIterator::SKIP_DOTS

PHPBB3-12268
[ticket/12268] Do not search in folders starting with a dot

PHPBB3-12268
[ticket/12268] Move class out of extension namespace and rename it

PHPBB3-12268
[ticket/12268] Rename class file to recursive_dot_prefix_filter_iterator.php

PHPBB3-12268
[ticket/12268] Do not use substr but just compare the character

PHPBB3-12268
[ticket/12289] Add viewtopic template events for posts specific custom notices

These events allow extensions to add own posts specific notices-alike info.

PHPBB3-12289
Merge remote-tracking branch 'rxu/ticket/12289' into develop-ascraeus

* rxu/ticket/12289:
  [ticket/12289] Add viewtopic template events for posts specific custom notices
Merge remote-tracking branch 'nickvergessen/ticket/12268' into develop-ascraeus

# By Joas Schilling
# Via Joas Schilling
* nickvergessen/ticket/12268:
  [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
[ticket/12292] Fix syntax error in admin.css

PHPBB3-12292
Merge remote-tracking branch 'VSEphpbb/ticket/12292' into develop-ascraeus

* VSEphpbb/ticket/12292:
  [ticket/12292] Fix syntax error in admin.css