Deep.Portals

Add an ability to mirror links from another, Deep inside this deep.

May be done as deep package at first.

It should work with similar fashion as minilinks, but all links, loaded by all queries should be recreated in Deep using separate type tree.

For example, it may be done using Portal link, which will have another Type of root links connected to it.

For example, Portal link may contain new Type that represent type system of another Deep.

There also should be `PortalSubscription` and `PortalQuery` links that will load desired links from another deep.

This may be useful for packages that have been completely protected by hosting them in the controlled by owner of the package environment.