add graph addVertex with no args

Signed-off-by: Alex McCaskey <mccaskeyaj@ornl.gov>

python/py_graph.cpp

@@ -45,6 +45,13 @@ void bind_graph(py::module &m) {
             g.addVertex(m);
           },
           "")
+      .def(
+          "addVertex",
+          [](xacc::Graph &g) {
+            HeterogeneousMap m;
+            g.addVertex(m);
+          },
+          "")
       .def(
           "setVertexProperties",
           [](xacc::Graph &g, const int index,