`DomainPool`'s should have distinct names

[cgevans]

Different domain pools can have the same name, but different properties, which does not appear to be the right use of them.

When this is the case, it appears that searches will actually work correctly, without throwing any errors, so long as the Design was created with code. However, loading a Design from a file will result in the pool assignments being wrong. This will then cause potentially subtle breakages (for example, sequences of the wrong length being assigned to domains).

I'm working on a minimal example.

It would probably be useful to check to ensure that domain pools in a system do not have the same name, particularly before saving a design file or starting a search.