Head token in Modex rules sub-automatons

One should be able to define and use a head token in sub-automatons.

Currently, you define and use a subautomaton like that:

```
define subautomaton NounGroup {
pattern=$DET? ($ADV{0-2} $ADJ){0-2} ($NC){0-2} $NC
}

@InfinitiveVerb::%NounGroup:SYNTACTIC_RELATION:
+!GovernorOf(right.1.4,"ANY")
+GovernedBy(trigger.1,"PrepInf")
+CreateRelationBetween(right.1.4,trigger.1,"COD_V")
=>AddRelationInGraph()
=AddRelationInGraph()
=