Basedata import - support polygon and polyline files

[shawnlaffan]

A reasonable amount of distributional data is provided as polygons, for example the IUCN range maps.

It should be possible to import these using a polygon intersection approach, with a fishnet polygon layer used to define the cells, and the coordinate taken from the fishnet centroids.

The fishnet could be dynamically updated to support multiple file imports, e.g. if two data sets have differing extents. This could be done using the bounding boxes.

http://www.gdal.org/classOGRGeometry.html#a83adb426e79958c90aecb418d91c765c

update 2018-11-29
The process can also work with polylines, so include them too.

2018-12-06, remaining work:

• Add geometry properties area and length to field name options. If not used then use binarise counts approach.
• Throw exception when basedata has zero cellsize for an axis that uses the shape x or y coordinates. We cannot build a fishnet for zero sized axes.
• Check that group axes include :shape_x and :shape_y, and build fishnet accordingly (e.g. if user specifies a text axis, then :shape_y then :shape_x).

[shawnlaffan]

Intersection process is very slow for some data sets, even when spatial indexes are set. This is of the order of minutes, where ArcGIS Pro takes a few seconds.

One cause is multipart polygons with many vertices. Making these single part appears to help, but needs to be done outside the system for now. ogr2ogr has an explodecollections option to do this, but I cannot find it in the OGR API.

Multi-resolution fishnets might be worth trying.

If we only need presence/absence and basedata cells are square then we could also rasterise instead.
https://gdal.org/gdal__alg_8h.html#adfe5e5d287d6c184aab03acbfa567cb1

[shawnlaffan]

Faster approach for binary (presence only) case in cfbf327

Need to look at using this as the default. Could use special fields for area and length, as per current approach for x, y, z and m coords. If :area and :length are not used for any of the data fields then we don't need geometry properties for the sample counts.

[shawnlaffan]

Mark as fixed.
Test failures are appveyor/chocolatey related.