ArcSDE DataStore requires ESRI jars to compile

ArcSDE was removed from the the build since it failed an IP check due to the need of having to have the ESRI ArcSDE Java API available to compile.

It was agreed with the OSGEO mentors that creating a stub for the API with only the needed classes and methods to avoid compile errors, without ever looking at the actual esri jars nor their javadocs does not constituent reverse engineering and thus could be added as a subproject of the arcsde plugin and make it compile against the stub.