Raises error in get_status if is not a valid resource
Adds combined confidence to combined predictions
Adding with_confidence to multimodels' predictions

- with_confidence argument to add combined confidence to multimodels
- Adding clarifying comments
- Checking preconditions in multivotes methods
- Refactoring complex computations
Bug fixing: public datasets can now be retrieved
Changes version number to 0.5.3
Adding tests for prediction combination and public datasets
Changes version to 0.5.2 and adds missing files