remove unlogical operation catching
method decorator tests
fix decorator problems in class methods (at least partially, there are problems with @staticmethod and @classmethod)
method decorator as class tests
fix problems with class method decorators
move descriptors out of classes into their own file
tests for #272, not existing method decorators in combination with super on __init__
ignore decorators if cannot be found (also get rid of DecoratorNotFound exception), fixes #272