Introduce the proof judgement ADT

src/main/scala/lisa/kernel/Printer.scala

src/main/scala/lisa/kernel/proof/SCProofChecker.scala

...ain/scala/lisa/kernel/proof/SCProofCheckerJudgement.scala

src/test/scala/lisa/kernel/ProofTests.scala

src/test/scala/lisa/proven/SimpleProverTests.scala

src/test/scala/test/ProofCheckerSuite.scala