Hide signature of the users per group

Need fix this first to work: https://github.com/mybb/mybb/issues/642
Or change $usergroup['signhide'] == 0 to $mybb->usergroup['signhide'] == 0 in functions_post.php

Original Thread: http://community.mybb.com/thread-153859.html

Ps. Please disregard the other pull request https://github.com/mybb/mybb/pull/643

Thanks