Closure support for plugins

Plugins can add hooks in the form of Closures to speed up develoment of
smaller plugins.
Removing spacing
Adding support for class methods as well as closures.

Class methods can be passed as an array. You can use either instance or static methods. To use an instance method, consider the following:

    class TestClass
    	{
    		function test($page)
    		{
    			$page = str_replace("<div id=\"content\">", "<div id=\"content\"><p>Hello World!<br />This is a sample MyBB Plugin (which can be disabled!) that displays this message on all pages.</p>", $page);
    			return $page;
    		}
    	}

    	$obj = new TestClass();

    	$plugins->add_hook("pre_output_page", array($obj, 'test'));

 To use a static method, simply pass the class name as the first array parameter and the method name as the second.
Removing stray echo
Adding remove_hook functionality.
Adding custom cache rebuild functions
This allows plugin authors to easily include their own rebuild/reload function if they add a cache
new backup file naming scheme: backup__yymmdd_hhmmss_random(.incomplete).sql(.gz)
mysqli optimizations
Merge branch 'feature' of https://github.com/mybb/mybb into feature
Fixing code style of object support for plugins.

Signed-off-by: Euan Torano <euantorano@gmail.com>
Adds last visit and online status to showteam.php
Adds last visit and online status to showteam.php

Removes additional space between icon and username.
Merge branch 'feature' of https://github.com/mybb/mybb into feature
Support for BIT(1) fields by checking if the value is numeric and not quoting if so.

Signed-off-by: Euan Torano <euantorano@gmail.com>
Merge branch 'feature' of https://github.com/mybb/mybb into feature-bit-field-support
Fixing code style.

Signed-off-by: Euan Torano <euantorano@gmail.com>
Add support for ISO 8601.
Delete user improvement

Improves the method for use deletion.
Adds last visit and online status to showteam.php

Hide last visit when user is invisible and current user cannot see
invisible users.
Fixes #216

Fixes #216: Instant activation not working as expected