[ticket/12531] Restore default topic link functionality in subsilver2

PHPBB3-12531
[ticket/12555] Allow to set canonical URLs to avoid duplicate content

PHPBB3-12555
[ticket/12555] Add canonical URl for memberlist mode=viewprofile

Avoids duplicate content of:
* memberlist.php?mode=viewprofile&u=user_id
* memberlist.php?mode=viewprofile&un=username

PHPBB3-12555
[ticket/12555] Add canonical URL for viewforum

Avoids duplicate content of:
* viewforum.php?f=forum_id
* viewforum.php?f=forum_id&start=0

PHPBB3-12555
[ticket/12555] Add canonical URL for viewtopic

Avoids duplicate content of:
* viewtopic.php?t=topic_id
* viewtopic.php?f=forum_id&t=topic_id
* viewtopic.php?f=forum_id&t=topic_id&hilit=highlight_string
* viewtopic.php?f=forum_id&t=topic_id&view=unread
* viewtopic.php?f=forum_id&p=post_id
* viewtopic.php?f=forum_id&t=topic_id&start=0

PHPBB3-12555
[ticket/12572] Fix JS error when alert message title is undefined

JS console reports error in core.js:
TypeError: alert is undefined
alert.hide()
when res.MESSAGE_TITLE is undefined.

PHPBB3-12572
[ticket/12585] Don't check the cron on each page load

PHPBB3-12585
Merge pull request #2480 from rxu/ticket/12572

[ticket/12572] Fix JS error when alert message title is undefined

* rxu/ticket/12572:
  [ticket/12572] Fix JS error when alert message title is undefined
Merge pull request #2468 from nickvergessen/ticket/12555

[Ticket/12555] Make use of canonical urls to avoid duplicate content

* nickvergessen/ticket/12555:
  [ticket/12555] Add canonical URL for viewtopic
  [ticket/12555] Add canonical URL for viewforum
  [ticket/12555] Add canonical URl for memberlist mode=viewprofile
  [ticket/12555] Allow to set canonical URLs to avoid duplicate content
[ticket/12531] Add some line breaks to really long lines

PHPBB3-12531
[ticket/12585] Use a 5 minutes interval instead of 10 minutes

PHPBB3-12585
Merge pull request #2490 from Nicofuma/ticket/12585

[ticket/12585] Don't check the cron on each page load

* Nicofuma/ticket/12585:
  [ticket/12585] Use a 5 minutes interval instead of 10 minutes
  [ticket/12585] Don't check the cron on each page load
Merge pull request #2444 from VSEphpbb/ticket/12531

[ticket/12531] Restore default topic link behavior to subsilver2

* VSEphpbb/ticket/12531:
  [ticket/12531] Add some line breaks to really long lines
  [ticket/12531] Restore default topic link functionality in subsilver2