Previously, with my Samsung Galaxy S5, I was able to select a custom MP3 file for my text message notification tone. However, with my new S7 Edge this option seems to be gone. I was able to add the mp3 file to the phone's list of ringtones, but the Message+ app (and the Samsung Messages app) only allow a notification tone to be selected from a very restricted list with no evident way to add a new tone. Is there a way to add my preferred sound to the list?