[ticket/12400] Add viewforum event to modify topics data

The event allows extensions to use and/or modify topics list and/or
topics data before dumping out the viewforum page.
For extensions which operate with viewforum page, f.e. if the topics list
and data is needed to retrieve, add, modify additional topics info
before the output loop.

PHPBB3-12400
[ticket/12401] Pass more data to core.viewtopic_modify_post_row event

$topic_data array is used in viewtopic.php to populate $post_row template
block array data. Although $topic_data is not being passed
to core.viewtopic_modify_post_row event for modifying/adding
$post_row data in it. So, pass this array to the event.
Also, total_posts is added.

PHPBB3-12401
[ticket/12191] Move notification options to bottom while installing

Move "ucp>board preferences>edit notification options" to bottom while
installing.

PHPBB3-12191
[ticket/12391] Assign variables to core.posting_modify_template_vars

Assign variables to event "core.posting_modify_template_vars".
Also, fix a couple of typos.

PHPBB3-12391
[ticket/12397] Fix sql_unique_index_exists doc block

db_tools::sql_unique_index_exists() searches for unique indexes but not
primary key indexes.

PHPBB3-12397
Merge pull request #2310 from n-aleha/ticket/12397

[ticket/12397] Fix sql_unique_index_exists doc block

* n-aleha/ticket/12397:
  [ticket/12397] Fix sql_unique_index_exists doc block
Merge branch 'develop-olympus' into develop-ascraeus

* develop-olympus:
  [ticket/12397] Fix sql_unique_index_exists doc block
Merge pull request #2300 from rxu/ticket/12400

[ticket/12400] Add viewforum event to modify topics data

* rxu/ticket/12400:
  [ticket/12400] Add viewforum event to modify topics data
Merge pull request #2301 from rxu/ticket/12401

[ticket/12401] Add $topic_data array to core.viewtopic_modify_post_row event

* rxu/ticket/12401:
  [ticket/12401] Pass more data to core.viewtopic_modify_post_row event
Merge pull request #2304 from n-aleha/ticket/12191

[ticket/12191] Move notification options to bottom while installing

* n-aleha/ticket/12191:
  [ticket/12191] Move notification options to bottom while installing
Merge pull request #2305 from n-aleha/ticket/12391

[ticket/12391] Assign variables to core.posting_modify_template_vars

* n-aleha/ticket/12391:
  [ticket/12391] Assign variables to core.posting_modify_template_vars