@Override
        public Object add(final GeoPrimitive item) {
            return null;
        }
An abstracted Map Layer which allows to handle a group of related geo objects on a map layer
together.
<br>
Methods of this class allow adding, removing, hiding/showing, ... of objects onto the layer in
a map-like fashion (means: using a key-GeoItem-concept).
Touch handling is also provided.
<br>
The abstract layer is connected towards a concrete map layer implementation by using the
setProvider method

@param <K> key class to use when placing and handling map geo objects on this layer
main/src/main/java/cgeo/geocaching/unifiedmap/geoitemlayer/GeoItemLayer.java