Patch to enable concrete Geometries instead of AbstractGeometry

As in previous issue, where was not possible to specify a concrete TimeInstant in om:phenomenonTime, I had the same problem in **sams:shape** where is not possible to specify a concrete _Geometry_. Following the previous patch I created a new one to solve this new issue.
I appended the following file to `./schemas/src/main/patches/ogc.patch`.

[abstractGeometry.patch.txt](https://github.com/highsource/ogc-schemas/files/449026/abstractGeometry.patch.txt)

I hope it helps.

Best regards

Start with schemas/src/main/patches/ogc.patch and compare the attached abstractGeometry.patch.txt with the earlier TimeInstant change described in the issue. Verify that the schema change allows sams:shape to use a concrete Geometry rather than only AbstractGeometry; done when the patched schema represents that concrete type correctly.

Written by the indexing model from the issue text.