Added spatial index to OverlayNG PolygonBuilder.placeFreeHoles

[arriopolis]

This PR adds a spatial filter to the polygonbuilder that is part of overlayng. This was already suggested in a comment present in the previous version.

I did some performance measurements too, to see how much time it saves. For the tests, I computed the difference between two MultiPolygons, one being a region and the other being lakes and rivers inside that region, both taken from OpenStreetMaps. Here are the performance results:

Region	Old time (ms)	New time (ms)	Data set
Zuid-Holland	194	189	zuid-holland.zip
Netherlands	902	903	netherlands.zip
Spain	1286	1168	spain.zip
Germany	2774	2163	germany.zip
France	4489	3322	*

*The data set for France is too big to upload, it's available upon request.

For the measurements, I took the average of five runs. I also checked that the areas of the resulting shapes match exactly in both runs.

[dr-jts]

Looks like a good improvement. Is there a particular reason you chose to use HPRTree - e.g. performance or memory usage? (It does seem like a good choice - just curious if you compared it to say STRtree).