Rename all uses of wasRecentlyAudible to recentlyAudible.
Add missing recentlyAudible properties.
Change QtQuick slots to simple functions.
Change affected demobrowser example.
Adjust documentation for the API.

Change-Id: I5a6f7b8384c0b7e34afaa5c412a5543c210d3ef9
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>
Reviewed-by: Michal Klocek <michal.klocek@theqtcompany.com>