Drastic simplification of Phases/Pipelines

src/main/scala/leon/LeonPhase.scala

src/main/scala/leon/Main.scala

src/main/scala/leon/Pipeline.scala

src/main/scala/leon/Settings.scala

src/main/scala/leon/verification/Analysis.scala

src/main/scala/leon/verification/AnalysisPhase.scala

src/main/scala/leon/verification/DefaultTactic.scala

src/main/scala/leon/verification/VerificationReport.scala

src/test/scala/leon/test/ValidPrograms.scala