Fix <label> position for multi checkbox so clicking on titles checks the boxes.  Also implements ability to do a natural sort on taxonomies.

First item is a small bug fix -- switch the location of the initial <label> for multi checkboxes so that clicking the label checks the checkbox.

Second item is bigger - It implements ability to specify natural_sort as part of the metabox fields for taxonomies.  This means that if numbers are part of a taxonomy they'll be sorted "naturally" instead of the default way.

i.e. if you specify "natural_sort" => true as part of the metabox array(), instead of this:

1, 10, 2, 3, 4, 5, 6, 7, 8, 9,

you will get this

1, 2, 3, 4, 5, 6, 7, 8, 9, 10