Added acf/get_post_id helper

Signed-off-by: Elliot Condon <e@elliotcondon.com>
Updated API functions to use acf/get_post_id filter

Signed-off-by: Elliot Condon <e@elliotcondon.com>
Image field: Fixed JS error caused by new updates to library

Signed-off-by: Elliot Condon <e@elliotcondon.com>