Refactoring of solvers.

src/main/scala/leon/AbstractZ3Solver.scala

src/main/scala/leon/Analysis.scala

src/main/scala/leon/Extensions.scala

src/main/scala/leon/solvers/ParallelSolver.scala

src/main/scala/leon/solvers/RandomSolver.scala

src/main/scala/leon/solvers/TimeoutSolver.scala

src/main/scala/leon/solvers/TrivialSolver.scala

src/main/scala/leon/solvers/z3/AbstractZ3Solver.scala

src/main/scala/leon/solvers/z3/FairZ3Solver.scala

src/main/scala/leon/solvers/z3/Z3ModelReconstruction.scala

src/main/scala/leon/synthesis/SynthesisPhase.scala

src/main/scala/leon/testgen/CallGraph.scala

src/main/scala/leon/testgen/TestGeneration.scala