@Override
    public void onPrepareSubMenu(@NonNull final SubMenu subMenu) {
        if (callback == null) {
            return;
        }
        addWaypoints(subMenu);
    }
Creates a new instance. ActionProvider classes should always implement a
constructor that takes a single Context parameter for inflating from menu XML.

@param context Context for accessing resources.
main/src/main/java/cgeo/geocaching/ui/WaypointSelectionActionProvider.java