Add implicit conversion to DSL

Add an implicit conversion from Option[T] where T is viewable as a
ValueNode to Option[ValueNode].

This makes it so the following is possible: `val x: Option[ValueNode] =
Option[String]("test")`, which can be very useful in some cases (e.g.
when manipulating string types directly, ending up with Option[String]
types, and putting them into arrays or objects).