Added distributed generation of nodes and edges files

[krisgeus]

Hi Friso,

Halfway done i think. Needs some TLC to finalize and maybe simplify, but it's a first working draft. Nodes are finished, relationships need some work to convert id's into rownum of the nodes.

See the TODO's if you want to work on it during my holiday.

Cheers Kris

[friso]

Did you run any regression on the existing batch import stuff, as it doesn't have any tests (I reserve the right to have no tests on demo code). I am pretty sure that some of the API changes from 1.6 to 1.8.