Make Graphhopper memory settings available

[PGWelch]

Graphhopper has different settings which control its memory usage. Using ODL Studio with a very large road network graph (2GB+) gives an out-of-memory exception even on a 64 bit machine. We need to expose the different graphhopper memory settings through ODL Studio so we can set it to use less memory (e.g. the mobile configuration) for larger road network files.