Preserve z coordinate in h2geodb (init WKBWriter with three dimensions)

Hi Karel, this pull request just changes the WKBWriter initialization in h2geodb's WKB class to use three dimensions instead of two. Previously z coordinates were not preserved when writing JTS geometries to WKB. After this patch, z coordinates survive round trip serialization to WKB. All tests still pass. Do you see any problem with merging this change?