Redesigned JSysCallConnector, to rely more on CallConnector.

Add Structural arcs to avoid stopping the traversal when a pseudo-predicate (i.e. return) has objects connected to it.

Add value dependency between the active exception definition and its throw/exception return statement.

Group actions before applying the ExpressionObjectTreeFinder and make grouping actions by root idempotent.

* TotalDefinition now can be connected to field declaration or total definition.

* VariableAction has 0..1 root OTs.
* VariableAction no longer has expressions, but has its kind of variable and name (in the future possibly type).
* Simplified checks and functions as a result

* VariableAction stores pending connections between trees.
* Update JavaParser from 3.17.0 to 3.19.0
* Object trees in assignments and return statements are linked to the appropriate expressions.
* Return trees are linked interprocedurally.
* ReturnStmt variable actions are now all generated by VariableVisitor.
* CallNode.Return are now generated by VariableVisitor instead of the SDG after the interprocedural finders.
* Actual-in nodes are now generated based on the expressions used, and then linked to the actual-in generated by the InterproceduralUsageFinder.
* We now accept calls as scope or argument of another call.
* ClassGraph is now a singleton. ClassGraph#newInstance() generates a new one.
* ClassGraph can generate a complete ObjectTree for a given type.
* MemberNode's parent can now be any node, and can be set after creation.
* New slicing algorithm for the JSysDG.
* Added interprocedural object-flow arcs.
* Added ObjectFlow and Flow dependency arcs.
* Introduced test to guarantee that interprocedural arcs are either input xor output.
* Updated tests

* JSysPDG: inserts IO and Member nodes before generating data dependencies.
* ObjectTree is now a real tree.
* ObjectTree has string and node iterables.
* VariableAction can be cloned with #createCopy(), the graphNode is set to null.
* VariableAction.Movable can't have object tree, getter obtains inner's.

* IAF now use a map of VariableAction instead of a set of StoredAction.
* They contain a map with stored actions.
* In their state, they accumulate the tree of repeated actions.

Resolve "Flag `-o` does not work"

Closes #47

See merge request !55

Fix bad smells

Closes #53, #52, and #54

See merge request !57