feat (root types) : add abstract root types in concerto ns

[dselman]

Signed-off-by: Dan Selman [email protected]

Issue #228

Adds abstract types to the system concerto namespace:

namespace concerto

abstract concept Concept {}
abstract asset Asset {}
abstract transaction Transaction {}
abstract participant Participant {}
abstract event Event {}

[jeromesimeon]

Excellent! Could we add something based on the example in the original issue as a test?

[jeromesimeon]

👍