Introduce plays! and relates! and owns! to query direct connections

[kim-tno]

Description

We would like to be able to query directly played/related/owned types, without inheritance.

match $p isa person; $r($t: $p) isa employment; $t plays! employee; get $t;

The exclamation mark raises an error.

Additional information

It would be nice if this were possible and returned only the directly owned/related/played connections and excluded the inherited ones.

[flyingsilverfin]

I've inverted this issue to reflect the closes desirable feature.