Proof loading / saving

Loading

1. (various ways a ProblemLoader gets created)
2. AbstractProblemLoader#load() sets up the environment (creating a directory for Java source files, unzipping the proof, reading taclet definitions, ...)
3. #createProofObligationContainer() creates the proof obligation
4. #createProof() creates a ProofAggregate object based on the obligation
5. #loadSelectedProof() replays the proof steps using IntermediateProofReplayer

Saving

Is done in OutputStreamProofSaver.