Feature space visualization tool + side by side gifs visual

[SunehB]

Description of the change:
Added functions fit_in_feature_space and _snap_feature_space in visualizer.py to visualize the learned decision boundary in the feature space
Added function combine_gifs to visualize the learned decision boundary gifs side by side
Added test_feature_space in test_visualizer.py

Motivation for the change:
We wanted a way to visualize gifs side by side
Visualizing the decision boundary in the feature space can show how the network transforms data to make it linearly separable

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient test coverage
• Docs updated
• Commit messages sensible and descriptive

[gallettilance]

Please:

1. adjust the test
2. add to the readme
3. fix linting issues
4. address comments

I know that's a lot - no rush! :)