ObjectTree: make fields into arrays of Strings.

- The previous approach used a single string, with fields separated by dots.
- The inclusion of packages in class names thwarts the previous approach.

* Simple enums, with empty constructors.
* Initializations are not handled.

Assumptions: there are no circular dependencies in initialization of static variables and enums are immutable.

* Summary arcs are generated correctly for actual-out with multiple actions.
* Properly detect optional actions.
* Fix type insertion at incorrect level in object trees.
* Constructors may throw exceptions.
* Dynamic initializers are marked as implicit.
* The LHS of an operation assignment is included in the ExpressionObjectTreeFinder (e.g. `a += 10`).
* Admit calls from dynamic initializers.
* Removed unused utility methods.

ExpressionObjectTreeFinder will now locate the correct VA, by searching for the matching call or expression.

Slicing criterion can include a variable. Multiple criteria can be included for a single file.

Add polymorphic calls

See merge request !61

* Call targets are computed based on static types (same as variable action's dynamic types).
* Usage and definition finders now deal with accumulating information in the same variable action ('-arg-in-' or '-scope-in-'). That variable action is created in the VariableVisitor, and the transference is prepared at the end of the finder, instead of with each handleActualAction.
* ObjectTree: pattern now accepts any variable, including fake patterns like ('-root-' or '-arg-in-')
* Tests updated

# Conflicts:
#	sdg-core/src/main/java/es/upv/mist/slicing/nodes/VariableAction.java

* Some searches in object trees may return multiple nodes (e.g. "var.A.x" and "var.B.x" for "var.x")
* Only leaves in object trees can be the target of summary arcs.
* Polymorphic nodes aren't interconnected with data dependencies.
* ClassGraph's map now split into kinds of vertex.
* ClassGraph's vertex now generic.
* Polymorphic member nodes cannot be leaves in object trees.

Dynamic types are computed from the descendants of the static type, without further analysis.

Update JavaParser and remove bug workaround.

Closes #60

See merge request !59

Object flow and trees

See merge request !58

* Some assertions changed to Illegal{State,Argument}Exception.

* Unified both summary arc analyzers
* Deleted unused code.
* Converted checks into assertions
* Removed some bad patterns, including a possible bug in BinaryExpr handling.