Create layers for layout graphics

Idea created by jessemaps on Jul 28, 2011
    Map layouts can often include many legend items, text, images, charts, and other graphics placed in the page layout. Many of these features can be overlapping and while one can arrange objects forward and back, it would be very helpful to include multiple layers to help organize and manage graphics on the layout.
    Besides helping with basic organization, including graphics layers that one can turn on or off would allow there to be different sets of graphics for different map bookmarks, versions, or pages (with DDP).
    The graphics layers should fit right in the table of contents and be ordered above and below data frames (but likely not within a data frame).