[FIX] remove deprecated jQuery.isFunction()
Relates: https://avan.tech/item98009
Notes: We still have warnings of this type ($.isFunction is deprecated) that are coming from two libraries:
- jquery-timepicker-addon which is in the replacement process here.
- jquery-plugins/colorbox which appears to be inactive, as its repository shows no recent activity over the past three years. It might be prudent to explore alternative options as a potential replacement.