Johan demo changes

This PR is pretty stuffed. It includes the following stuff:

* NetCdfReader custom formats with appropriate defaults
* A variance calculator for tiles for raster/op/local.
* A time window based spark op local temporal functionality with a custom DSL for mean, max, min and variance.
* Fixed the Spark Cost-Distance for graphs so that's working fully now (Bug was in edges creation + turning tile coords to vertex id)

It has been merged with the master branch.