moving the dropdown to only post 3.5 versions
major refactor of the metaboxes, so extend an abstract class. This puts filtering text fields in the metaboxes
making the new metaboxes, 3.4 metaboxes are now referred to as "foux" metaboxes, because they continue to be used for the Media Modal in 3.5 and after
updating readme to describe the new filtering of taxonomies in metaboxes