[ticket/11795] Redo form elements auto-focus

Use data-focus attribute for forms to focus elements
when document is loaded instead of adding JavaScript

PHPBB3-11795
[ticket/11795] Use data-reset-on-edit attr to reset elements

Use data-reset-on-edit attribute to reset other inputs
when editing input with data.

Do not unbind event (old code unbound it after one use for
no reason)

PHPBB3-11795
[ticket/11795] Get rid of onload_functions

Get rid of onload_functions and onunload_functions
Scripts should use $(document).ready() instead

PHPBB-11795
[ticket/11795] Get rid of pagination JS variables

Move pagination variables to data attributes
Replace A_BASE_URL with BASE_URL and use TWIG to escape it

PHPBB3-11795
[ticket/11795] Move PM popup JS to forum_fn.js

Move PM popup JavaScript from overall_header to forum_fn.js
Use TWIG to escape PM popup URL

PHPBB3-11795
[ticket/11795] Use phpBB template syntax instead of TWIG

PHPBB3-11795
[ticket/11795] Move MSN scripts to forum_fn.js

Move MSN scripts to forum_fn.js
Rewrite MSN scripts to remove duplicate code

PHPBB3-11795
[ticket/11795] Replace TWIG with phpBB syntax in ACP

PHPBB3-11795
[ticket/11795] Move find user JS to forum_fn

Move JavaScript from user search results to forum_fn.js

PHPBB3-11795
[ticket/11795] Remove outdated comment from forum_fn.js

This comment is no longer relevant because function was rewritten

PHPBB3-11795
[ticket/11795] Remove PM popup

PHPBB3-11795
Merge pull request #1666 from cyberalien/ticket/11795

Move JS from html files to forum_fn.js
Merge remote-tracking branch 'upstream/develop' into develop