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.