Let PAC have one proof_attempt and remove goals When the ProofAttemptCofiguration only has one proof_attempt, there can only be a single goal. This can be retrieved through the proof_attempt.

Handle hets' "nothing to prove" return value.

Rename the Evaluator classes to Importer.

Move lib/hets/*/evaluator.rb to lib/hets/*/importer.rb Renaming the classes will be done in another commit.