Actually support domain on Reference field
Currently the domain on reference fields are not enforced on server-side. But also it mainly does not work because it is not possible to setup a domain for different target model. I propose to use as domain a dictionary with as key the target model name and as value the domain to apply. The validation on server side will create a single OR-ed domain out of the dictionary with a last clause which match all target without keys. The client which only need the domain for a specific target will just take it from the key of the attribute.