[2.0] Spatial Types Support

[jspuij]

EF does not support the full range of spatial types, nor both conversion directions (model to DB and vice versa).
There is no support whatsoever for EF Core. Needs to be done as well. Make a nice Interface for abstraction.

[bytefish]

Getting Spatial Types to work correctly with ASP.NET Core OData was a little painful, I have written it down here:

• https://www.bytefish.de/blog/aspnet_core_odata_example.html#extending-partial-classes-with-microsoftspatial-properties

@robertmclaws I am not sure, how something similar could be added to Restier 2.0, because it contained a lot of working around, but I‘d be happy to help.