Systematic treatment of Identifier/Definition owners

src/main/scala/leon/frontends/scalac/CodeExtraction.scala

src/main/scala/leon/purescala/Common.scala

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

src/main/scala/leon/purescala/FunctionClosure.scala

src/main/scala/leon/purescala/PrettyPrinter.scala

src/main/scala/leon/purescala/RestoreMethods.scala

src/main/scala/leon/purescala/TreeOps.scala

src/main/scala/leon/utils/ScopingPhase.scala

src/main/scala/leon/xlang/XlangAnalysisPhase.scala