Argueview

- grounds and backing are now optional.

- added support for bar visualization within FeatureListVisualizer.
- updated screenshots
- fixed output for negative and neutral decision-classes

- added support for omitting features in the FeatureListVisualizer.

- fix data types of openml features in one example
- fix key names of labels of latent continuous target
- bump argueview-js version to 0.3.1
- finalize feature list visualizer

- fix data types of openml features in examples

- fix critical error with error checking
- add json exported pretty-print option