[ticket/11562] Convert marklist() to jQuery

PHPBB3-11562
[ticket/11562] Remove submit_default_button from forum_fn

Remove submit_default_button() and related functions
from forum_fn.js

PHPBB3-11562
[ticket/11562] Use jQuery in subPanels

PHPBB-11562
Merge pull request #1435 from cyberalien/ticket/11562

forum_fn.js cleanup