find better way instead of @Contracted

there needs to be a visitor implementation which takes a look for contract annotations:

1. check if class-invariant is available on the current class
   
2. check if any method has a pre- or postcondition
   
3. check if any descendant class has a class-invariant
   
4. check if any descendant class has method with a pre- or post-conditon
   
5. check if any implemented interface has a method with a pre- or post-condition
   
6. check if any interface descendant has a method with a pre- or post-condition

automatically annotate classes with @Contracted if a contract element was found.

(from [844ab0f65d191e9679791ee09e9b097990e18064]) find better way instead of @Contracted [#8 find better way instead of @Contracted] https://github.com/andresteingress/gcontracts/commit/844ab0f65d191e...