- Use SealedClassFixCore to define the AST rewrite required for the
  quick fix
- Use helper methods for retrieving the sealed type and permitted type
- Instead of 'problem.getProblemArguments()[0]', use the type
  declaration's identifier to get the simple name
- Add createCorrectionProposalFromCURewriteOperation(..) helper method

Signed-off-by: Roland Grunberg <rgrunber@redhat.com>