OA: Class OATask - Extension of adaption by new methods for pre- and postprocessing

[detlefarend]

Description/Motivation Class OATask shall be extended by further custom methods for pre- and postprocessing as part of adaptation.

Task list

• [x] 1. New custom method OATask._adapt_pre()
• [x] 2. New custom method OATask._adapt_post()
• [x] 3. Method OATask.adapt(): integration of new methods