Added a new addEdge method in SDFGraph.

The new method accept as parameters the two vertices between which we want an edge, their respective ports on which we want to connect the edge, the consumption and production rates and the delay of the edge to create.
Made the matchCopies map a private global variable available through getMatchCopies() for external use (such as in PiMM2SDF transformation).
Formating.
Added final static Strings for the keys of common inputs/outputs of workflow tasks (SDFGraphs and PiGraphs, scenarios...).

Those keys are available in every subclass of AbstractTaskImplementation, that is, in every workflow task we define.
Added a hasChanged boolean indicating whether the visited SDFGraph has been changed by the visitor or not.
+ formatting
Refactored input and output keys for Workflow tasks.
Formating.
Moved keys for inputs/outputs of workflow tasks from AbstractTaskImplementation to AbstractWorkflowNodeImplementation, in order for ScenarioNodes to use them. Also merged KEY_SDF_SCENARIO and KEY_PI_SCENARIO into KEY_SCENARIO, since we merged PreesmScenario and PiScenario into PreesmScenario.
Added a key for input/output MemoryExclusionGraphs and Sets of MemoryExclusionGraphs.
Added a key or input/output map of DAGs and MemoryExclusionGraphs (DAGsAndMemExs) and formatted.
Rewrote AbstractGraph.getHierarchicalVertexFromPath in order to handle calls where the given path contains the graph name.
Changed getArguments method in AbstractVertex to prevent from returning null.
If there no current ArgumentSet, we create and add one and return it.
Changed getVariables method in AbstractGraph to prevent from returning null.
If there no current VariableSet, we create and add one and return it.
Added new input/output keys for memory bounds.
Passed CodeRefinement encoding of file position from String to IPath.
Removed useless method.
Added tests to handle empty path refinements.
(Model) PURE_IN and PURE_OUT annotations become READ_ONLY and WRITE_ONLY
Refactored path variable name to refinementPath to avoid mixing with this.path.
Added a copy of new attribute refinement (which is now separated from the properties map).