Allow the nodes graph expression to rank by inbound degree

Currently the nodes graph expression only calculates inbound degree if the count(*) aggregation is applied to the function. This ticket will cause the nodes function to always calculate inbound degree and return the nodes in descending inbound degree order. A new top parameter will be added to only return the top N nodes with the highest inbound degree. The indegree field will be added to each node in the returned nodeset. The scoreNodes function will also be changed to use the indegree field rather than the count(*) field.