Add implicit constructors

* Small regression: only the last field declared in a constructor is included. This is expected, and will be solved with the new object dependencies.
* Integrate ImplicitNode as boolean in GraphNode.
* Updated tests
* Slice now allows the insertion of implicit instructions, but does not output them when generating the AST.
* Removed list of nodes from slice, as the map contains a superset of the information of the list.