! Properly fix issues with HTML in forum title and maintenance mode title...

This will do the following:
1. Sanitize maintenance mode title only where it's used. Trying to sanitize it in the admin center will result in it being sanitized multiple times since SMF htmlspecialchars()'s things before displaying the values for editing.

2. Use $context['forum_name_html_safe'] in place of $context['forum_name'] in many places where we're using it in the template. $context['forum_name'] is used too many places to have it sanitized all the time, plus it would be sanitized multiple times whenever you go to edit server settings.

Signed-off-by: Michael Eshom <oldiesmann@oldiesmann.us>