[ticket/13034] Fix the route generated for the frontend not in the phpbb root

PHPBB3-13034
[ticket/13034] Fix unit tests

PHPBB3-13034
[ticket/12963] Fix the list of migrations in database_update.php

Without this patch the finder grab all the class available in the ext
folder and not only the migrations. This change is backported for the one
done before to the cli tool db:migrate. (see the commit
3420f8f3201ac337434f73ee00bda6df7b378212)

PHPBB3-12963
[ticket/12963] Don't use static var in \extension\base\get_migration_file_list

The static var was global to all instance of \phpbb\base and so if two
different instances (for two different extensions) were created by the
same script they shared the same migrations list.

PHPBB3-12963
[ticket/12963] Load extensions migrations from /migration

PHPBB3-12963
[ticket/12963] Add unit tests

PHPBB3-12963
[ticket/13009] Remove legacy browser hacks

PHPBB3-13009
[ticket/13056] Move the arguments of the request class to the DI

PHPBB3-13056
[ticket/13061] Replace the service event.subscriber_loader by a compiler pass

PHPBB3-13061
[ticket/13062] Add viewforum.php core event to modify topic ids sql query

Event request: http://area51.phpbb.com/phpBB/viewtopic.php?f=111&t=45383

PHPBB3-13062
[ticket/13058] Add min value to jump to page input

PHPBB3-13058
[ticket/13064] Validate the migrations provided to migrator::set_migrations()

PHPBB3-13064
Merge remote-tracking branch 'Nicofuma/ticket/13058' into develop-ascraeus

* Nicofuma/ticket/13058:
  [ticket/13058] Add min value to jump to page input
Merge remote-tracking branch 'hanakin/ticket/13009' into develop-ascraeus

* hanakin/ticket/13009:
  [ticket/13009] Remove legacy browser hacks
[ticket/13040] Fix W3C validator warning in overall_footer.html

Added a non-breaking space to remove the following warning:
**Empty heading.**

```html
<h3 class="alert_title"></h3><p class="alert_text"></p>
```

PHPBB3-13040
Merge remote-tracking branch 'prototech/ticket/13040' into develop-ascraeus

* prototech/ticket/13040:
  [ticket/13040] Fix W3C validator warning in overall_footer.html
[ticket/13065] Fix rehashing of stored password hash in phpBB2 convertor.

PHPBB3-13065
[ticket/13019] Always accept a reason for deleting a post/topic.

PHPBB3-13019
[ticket/13019] Rename deletion reason label.

PHPBB3-13019
[ticket/13019] Do not hide reason field when deleting permanently.

PHPBB3-13019