Fix #72 - allow zooming in to level 19
Fix #72 - allow zooming in to level 19

dronekit/droneshare,dronekit/droneshare,dronekit/droneshare,SecureCloud-biz/droneshare,SecureCloud-biz/droneshare,PHELiOX/droneshare,PHELiOX/droneshare,SecureCloud-biz/droneshare,PHELiOX/droneshare,diydrones/droneshare,diydrones/droneshare,diydrones/droneshare