Extend ART to feature vectors

[ririnicolae]

Description

This PR extends ART to feature vectors. clip_values are now optional in classifiers. Clipping is only performed when these values are present. Constraints for images shapes have been removed. Attacks and defences were adapted to more general data shapes. Some attacks and defences that can only be applied on images now raise an error if a different data shape is provided. All these changes were tested on the Iris dataset with a small neural network model.

Closes #49

Type of change

Please check all relevant options.

• Bug fix (non-breaking)
• New feature (non-breaking)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Testing

• Add trained Iris models for testing and code for loading them
• Add unit tests for attacks, classifiers, wrappers and defences using Iris dataset

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[beat-buesser]

@ririnicolae Your code looks great! I found 3 newly commented lines, could we remove them?

[ririnicolae]

@beat-buesser Thanks for the review and for noticing those comments, I have removed them now!