[ticket/11786] Fix typo and ugly English in the notification system PHPDoc

The notification system contained two PHPDoc lines that needed improvement.

PHPBB3-11786
[ticket/11786] Fix PHPDoc documentation of a few events

Fixed some PHPDoc errors I noticed while working on the karma extension.
Mostly spacing issues or omitted characters, though there was one description
that made no sense at all.

PHPBB3-11786
[ticket/11786] s/@return void/@return null in content_visibility.php

The file phpbb/content_visibility.php still contained a few instances of
'@return void' in its PHPDoc blocks, fixed. Thanks to JoshyPHP for reporting.

PHPBB3-11786
[ticket/11786] Further improve wording in phpbb/notification/type/quote.php

Further improve wording in phpbb/notification/type/quote.php per suggestion of
imkingdavid.

PHPBB3-11786
[ticket/11850] Fix $user->page on pages through the controller

PHPBB3-11850
[ticket/11850] page_name contains controller request rather than query string

Fixing tests

PHPBB3-11850
[ticket/11850] Add test for outside of the phpBB directory

PHPBB3-11850
[ticket/11850] Fix extract current page test

PHPBB3-11850
Merge branch 'develop' of git://github.com/phpbb/phpbb3 into ticket/11786
[ticket/11786] Fix indentation in the PHPDoc of core.group_delete_user_before

The core.group_delete_user_before event had bad indentation in its PHPDoc.
Fixed.

PHPBB3-11786
[ticket/11691] Stagger the convertion of soft delete updates

PHPBB3-11691
[ticket/11691] Stagger user notification reconversion even more

PHPBB3-11691
[ticket/11691] Change detection of effectively_installed()

When start is set for a migration, it is not yet effectively installed.
So we just continue doing it...

PHPBB3-11691
[ticket/11691] Fix some more problems with softdelete update

* wrong order of arguments on sql_query_limit
* avoid "BIGINT UNSIGNED value is out of range" errors
* increase limit for the loop

PHPBB3-11691
[ticket/11691] Fix some minor comments

PHPBB3-11691
[ticket/11691] Add order by to the query

PHPBB3-11691
[ticket/11691] Fix typo in comment

PHPBB3-11691
[ticket/11691] Move purge code into new function

PHPBB3-11691
[ticket/11691] Fix table names and arguments/docs

PHPBB3-11691
[ticket/11852] Split filesystem and path_helper into 2 classes

PHPBB3-11852