* Migrated `NodeType`s to specific `GraphNode` child classes.
* Revamped creation of SDG
* Added ASDG and PSDG, based on the APDG and PPDG.
* Improved handling of variable usages, definitions and declarations.
* Added movable variable actions, that can be placed in a CFG node and
  then relocated to their own PDG node.
* Added fix-point and specific slicing algorithm to summary arc
  generation.
* Documentation of most methods (public and private).
* Removed unused elements.
* Fix possible errors by migrating all maps whose key is an AST node
  to IdentityHashMap.

Previously, those that did not perfectly match were discarded and left unconnected.

* DataDependencyArc: change style
* Exit/ReturnNode: removed variable extraction
* ESCFG: removed the method call as an exception source.

Other changes: corrections, improvements and API simplification

* Includes minor fixes to slicing criterion and slice to AST conversion
* Minor changes in logging, to avoid logging without error/warning

Side-effect: PDGTests cannot access GraphLog.

Added output node to method declaration + changed return to output

WIP: Added Naive summary arcs builder

Organize NodeType enum

* Added METHOD_EXIT
* Renamed METHOD to METHOD_ENTER
* Split VARIABLE_IN into FORMAL_IN and ACTUAL_IN.
* Split VARIABLE_OUT into FORMAL_OUT and ACTUAL_OUT.
* Removed exitNode from CFG and corresponding methods.

Resolve 6-method-call-nodes