Refactor Tegis/Cegis

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

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

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

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

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