Move Printable to core leon package. More classes implement it

src/main/scala/leon/Printable.scala

src/main/scala/leon/solvers/ADTManager.scala

src/main/scala/leon/solvers/Model.scala

src/main/scala/leon/solvers/templates/UnrollingBank.scala

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

src/main/scala/leon/synthesis/CostModel.scala

src/main/scala/leon/synthesis/InOutExample.scala

src/main/scala/leon/synthesis/Problem.scala

src/main/scala/leon/synthesis/Rules.scala

src/main/scala/leon/synthesis/Solution.scala

src/main/scala/leon/synthesis/graph/Graph.scala

...n/scala/leon/synthesis/strategies/CostBasedStrategy.scala

src/main/scala/leon/utils/FreeableIterator.scala