Master

Updated the code for a few changes to support EASY sorting of the levels.

1) TODO not sure how you wanted to handle it.. was the 

`sort_order` int(11) NOT NULL DEFAULT '0',    added to the Table structure for table `wp_pmpro_membership_levels`

2) Fixed what looked to be a bug for the orginal order by clause since if that condition was not true the order by would be skipped.