- had to add check for existing pdf's to allow their option value to be an integer.
- moved walker from custom_nav to this new file updated the code to work with wfc_meta_box_cases.php structure.
- moved the walker class to to its own file.
- edit admin css; it was hidding non image checkboxes.
- added form element on example CPT; checkboxes without images.
- removed wfc_helper_functions.php; moved all non-theme specific functions to better places.