Add graph-oriented version of the metamodel (suggested by Artur Boronat)

config/config.json

metamodels/BDD.km3

metamodels/BDDv2.ecore

metamodels/TT.km3

metamodels/ttc2019.metamodels/META-INF/MANIFEST.MF

metamodels/ttc2019.metamodels/models/BDDv2.ecore

metamodels/ttc2019.metamodels/models/BDDv2.genmodel

metamodels/ttc2019.metamodels/plugin.xml

...etamodels/src-gen/ttc2019/metamodels/bddg/Assignment.java

...c2019.metamodels/src-gen/ttc2019/metamodels/bddg/BDD.java

...tamodels/src-gen/ttc2019/metamodels/bddg/BDDGFactory.java

...tamodels/src-gen/ttc2019/metamodels/bddg/BDDGPackage.java

...metamodels/src-gen/ttc2019/metamodels/bddg/InputPort.java

...2019.metamodels/src-gen/ttc2019/metamodels/bddg/Leaf.java

...etamodels/src-gen/ttc2019/metamodels/bddg/OutputPort.java

...2019.metamodels/src-gen/ttc2019/metamodels/bddg/Port.java

...9.metamodels/src-gen/ttc2019/metamodels/bddg/Subtree.java

...2019.metamodels/src-gen/ttc2019/metamodels/bddg/Tree.java

.../src-gen/ttc2019/metamodels/bddg/impl/AssignmentImpl.java

...src-gen/ttc2019/metamodels/bddg/impl/BDDGFactoryImpl.java