Add a Count function to query language


There should be a way to query the graph to see how many nodes exist without printing all of the values. This can currently be achieved with _size(g.V( ).ToArray( )), but it should be implement in cayley as something like g.V( ).count( ), but the count function should be applicable to any type of call. For example, calling g.V( ).Tag(“source”).Out(“follows”).count( ) on the testdata.nq graph should return the number of people each person follows.