[ticket/13110] Add core event to the page_footer() function

Add core event to the page_footer() in includes/functions.php to allow
extensions handling overall page output before its displaying.

PHPBB3-13110
[ticket/13116] Interchange post and topic approval notification

PHPBB3-13116
[ticket/13123] Add events to allow modifying post data

PHPBB3-13123
[ticket/13119] Add another event which is triggered independent from actions

PHPBB3-13119
[ticket/13059] Add core event to generate_page_link()

Add core event to generate_page_link() to allow
overriding/modifying pagination URLs.
Event request: http://area51.phpbb.com/phpBB/viewtopic.php?f=111&t=45905

PHPBB3-13059
[ticket/13108] Add core event to the parse_attachments() function

Add core event to the parse_attachments() function in functions_content.php
to allow modifying/adding attachment template data.

PHPBB3-13108
Merge pull request #3015 from nickvergessen/ticket/13119

[ticket/13119] Add another event which is triggered independent from actions
Merge pull request #3012 from nickvergessen/ticket/13123

[ticket/13123] Add events to allow modifying post data

* nickvergessen/ticket/13123:
  [ticket/13123] Add events to allow modifying post data
Merge pull request #3004 from Senky/ticket/13116

[ticket/13116] Topic and post approval notifications got interchanged
Merge pull request #2999 from rxu/ticket/13108

[ticket/13108] Add core event to the parse_attachments() function
Merge pull request #2947 from rxu/ticket/13059

[ticket/13059] Add core event to generate_page_link()
Merge pull request #3000 from rxu/ticket/13110

[ticket/13110] Add core event to the page_footer() function