Use MER<> for CreateSpace and return Conflict/Created responses

[p-kaczynski]

Resolves #911

The check for ID seems to not be needed:
API.Features.Space.Converters.SpaceConverter.ToHydra
calls
DLCS.HydraModel.Space.Space_ctor
calls
DLCS.HydraModel.DlcsResource.Init
sets:

Id = BaseUrl + string.Format(uriTemplate, urlParams);

which uses:

[HydraClass(typeof(SpaceClass),
       Description = (snip),
       UriTemplate = "/customers/{0}/spaces/{1}")]
[Unstable(Note = "Under active development")]
public class Space...