OrientDB polymorphic vertices and edges iteration

New implementation much more efficient on g.getVertices('@class',
'MySubClass') and g.getEdges().

Furthermore there are new methods:

g.getVerticesOfClass("MySubClass"); //  POLYMORPHIC: GET MySubClass AND
SUBCLASS INSTANCES
g.getVerticesOfClass("MySubClass", false); // NOT POLYMORPHIC: GET ONLY
MySubClass INSTANCES

g.getEdgesOfClass("MySubClass"); //  POLYMORPHIC: GET MySubClass AND
SUBCLASS INSTANCES
g.getEdgesOfClass("MySubClass", false); // NOT POLYMORPHIC: GET ONLY
MySubClass INSTANCES