[ticket/12831] Optn to prevent setting HTTP headers

https://tracker.phpbb.com/browse/PHPBB3-12831

PHPBB3-12831
[ticket/12809] Fix select button and dropdown list items in RTL.

PHPBB3-12809
[ticket/12809] Remove obsolete rules and selector.

PHPBB3-12809
[ticket/12809] Restore text-align for the pagination.

PHPBB3-12809
[ticket/12671] Possibility to use NOT LIKE expression

PHPBB3-12671
[ticket/12794] Properly validate google+ field against valid character set

PHPBB3-12794
[ticket/12671] Possibility to use NOT LIKE expression

PHPBB3-12671
[ticket/12671] Possibility to use NOT LIKE expression

PHPBB3-12671
[ticket/12671] Possibility to use NOT LIKE expression

PHPBB3-12671
[ticket/12938] Remove the 'Download all attachments' feature.

PHPBB3-12938
[ticket/12943] Add core.phpbb_generate_debug_output core event

Add core.phpbb_generate_debug_output core event to allow extensions
outputting additional debug info.

PHPBB3-12943
[ticket/12953] Page title not updated when notifications are marked as read

PHPBB3-12953
[ticket/12671] Possibility to use NOT LIKE expression

PHPBB3-12671
[ticket/12831] reimplemented headers as array

https://tracker.phpbb.com/browse/PHPBB3-12831

PHPBB3-12831
[ticket/8064] Change the collation of topic_first_poster_name

PHPBB3-8064
[ticket/12938] Remove functional tests for 'Download all attachments'.

PHPBB3-12938
[ticket/12831] simplified code, upd event block

https://tracker.phpbb.com/browse/PHPBB3-12831

PHPBB3-12831
[ticket/12956] Ensure the contact columns have been added before using them

PHPBB3-12956
[ticket/12831] fix CS

https://tracker.phpbb.com/browse/PHPBB3-12831

PHPBB3-12831
Merge remote-tracking branch 'github-nicofuma/ticket/8064' into develop-ascraeus

* github-nicofuma/ticket/8064:
  [ticket/8064] Change the collation of topic_first_poster_name