Update set.php and fieldmulti.php

set.php=====
Deleted the fa class for the icon, now the fontawesome field type can be extended and used with any font-icon without conflicts. When fa class is used, it sets FontAwesome font-family and makes other fonts to not use own font-family.

fieldmulti.php=====
If user function finds no items, it returns
Warning: array_merge(): Argument #2 is not an array in site\wp-content\themes\theme\inc\options\framework\classes\control\fieldmulti.php on line 36