Add abstract decorators to properties and methods on the base classes.

Add the `@abstractmethod` decorator to all methods expected to be inherited on the derived classes, as well as below the `@property` decorator for all properties that should be implemented by all derived classes. A lot of the examples that require this change can be found by searching for `raise NotImplementedError("Implement this in the derived class")`, plenty of which can be found in `Wells.py`.
Ensure `@property` is above `@abstractmethod` for abstract properties.