Refactor Terminating to be more modular

src/main/scala/leon/purescala/Definitions.scala

src/main/scala/leon/purescala/ExprOps.scala

src/main/scala/leon/repair/Repairman.scala

src/main/scala/leon/synthesis/SourceInfo.scala

src/main/scala/leon/synthesis/Witnesses.scala

src/main/scala/leon/synthesis/rules/CEGISLike.scala

src/main/scala/leon/synthesis/rules/IntroduceRecCalls.scala

src/main/scala/leon/synthesis/utils/Helpers.scala