[ticket/9801] Allow display of page outside board directory on viewonline

Until now, the preg_match didn't take into account that a page might be
outside the board directory. After this change, the regular expression will
allow preceding dots and slashes. Paths like ../../test.php will be allowed.
The page will be unknown in viewonline.php and it will revert to index.php as
current page. However, the core.viewonline_overwrite_location event will
receive proper info of the page the user is on right now allowing a listener
to change the info that is being displayed.

PHPBB3-9801
[ticket/9801] Add viewonline_helper service to allow proper testing

The viewonline_helper service can and will be extended in the future which
will allow us to also test the viewonline page better.

PHPBB3-9801
[ticket/12662] Initial setup

PHPBB3-12662
[ticket/12662] Enable responsive linkslist for IE8

Also fixed arrow color

PHPBB3-12662
[ticket/12662] RTL (bidi.css) fixes

PHPBB3-12662
[ticket/12662] Fix rounding problems when detecting relative height

Firefox and IE round subpixels up, while webkit rounds down. So we have
to account for that.

PHPBB3-12662
[ticket/12662] Improve icons and footer links

PHPBB3-12662
[ticket/12662] Added ARIA functionality

PHPBB3-12662
[ticket/12662] Improve template checks

And changed _CLEAN to _SIMPLE, and move teamlink events

PHPBB3-12662
[ticket/12662] Update PR after ticket/12553 merge

Rebasing was a nightmare with all the code moving around between
commits. Hopefully this will merge without a rebase.

PHPBB3-12662
[ticket/12662] Fix recently merged PR changes lost in rebase

PHPBB3-12662
[ticket/12662] Change new event names and fix events.md

Previously merged PR said b4 instead of b5, also not alphabetical.

PHPBB3-12662
[ticket/12662] Use slack variable to determine line-break sensitivity

PHPBB3-12662
[ticket/12662] Reorder icon CSS rules alphabetically

Was getting a bit disorganized

PHPBB3-12662
[ticket/12662] Change CSS selectors to direct descendants for linklist

PHPBB3-12662
[ticket/12662] Remove inherited props from ddown-extendended

PHPBB3-12662
[ticket/12662] Fix responsive positioning of notifications dropdown

PHPBB3-12662
[ticket/12662] IE8 fixes

PHPBB3-12662
[ticket/12662] Add span containers to all usernames for consistency

PHPBB3-12662
[ticket/12662] Remove linklist container and update template events

PHPBB3-12662