Abstract and simplify edge definition?

Should we allow defining edges without defining id fields??

```
Foo as Node {
  blahId: ID<Blah>
} & OutboundEdges {
  blah: Edge<Foo.blahId>
}
```

to:

```
Foo as Node {
} & Edges {
  blah: OneToOne<Blah>
}
```

but this removes control from the developer and feels a bit opaque.