#6 the enum GeometryFunction got a String-field

The enum GeometryFunction got a String-field, whose value is the
corresponding postgis-function.
 #6 The postgis function is variable in appendGeometry()

In the method appendGeometry() the used postgis function depends now on
the field geometryFunction. As the parameters of the function are still
hard-coded, their order has to be changed as the contains-function is
not commutative.