foam.box.SelectorRegistry bug fix
foam.box.SelectorRegistry bug fix

`SelectorRegistry` should (and already did) store its own relay to delegate
service to provide a consistent namespace to clients. This facilitates:

```
var returnedBox = registry.register('foo'/* ... */);
/* ...
   elsewhere, where returnedBox is not accessible
   ... */
foam.box.SubBox.create({
  name: 'foo',
  /* ... */
}/* ... */).send(messageToFooService);
```

without name confusion between delegates. However, the box returned from
`SelectorRegistry.register()` must be portable to remote locations that are
bound to its delegates' contexts. Hence, return the box from
`selectorRegistrySelectedDelegate.register(...)`.

Naturally, both `register()` and `unregister()` needed to be refactored to
correctly re-find both delegate and local relay boxes.

foam-framework/foam2,TanayParikh/foam2,jacksonic/vjlofvhjfgm,jacksonic/vjlofvhjfgm,TanayParikh/foam2,foam-framework/foam2,foam-framework/foam2,TanayParikh/foam2,jacksonic/vjlofvhjfgm,TanayParikh/foam2,foam-framework/foam2,foam-framework/foam2