Added datagen, continued working on trees

src/main/scala/inox/datagen/DataGenerator.scala

src/main/scala/inox/datagen/GrammarDataGen.scala

src/main/scala/inox/datagen/NaiveDataGen.scala

src/main/scala/inox/datagen/SolverDataGen.scala

src/main/scala/inox/datagen/VanuatooDataGen.scala

src/main/scala/inox/evaluators/AbstractEvaluator.scala

src/main/scala/inox/evaluators/AbstractOnlyEvaluator.scala

src/main/scala/inox/evaluators/AngelicEvaluator.scala

src/main/scala/inox/evaluators/CodeGenEvaluator.scala

src/main/scala/inox/evaluators/DualEvaluator.scala

src/main/scala/inox/evaluators/EvaluationPhase.scala

src/main/scala/inox/evaluators/ScalacEvaluator.scala

src/main/scala/inox/evaluators/StreamEvaluator.scala

src/main/scala/inox/evaluators/TracingEvaluator.scala

src/main/scala/inox/evaluators/TrackingEvaluator.scala

src/main/scala/inox/solvers/EvaluatingSolver.scala

src/main/scala/inox/solvers/RawArray.scala

src/main/scala/inox/solvers/string/StringSolver.scala

src/main/scala/inox/solvers/unrolling/Quantification.scala

src/main/scala/inox/trees/CallGraph.scala