Fix/check pred step

[picciama]

PR Checklist

• [x] This comment contains a description of changes (with reason)
• [ ] Referenced issue is linked
• [ ] If you've fixed a bug or added code that should be tested, add tests!
• [x] Documentation in docs is updated

Description of changes

• fixed some plotting issues with violin plots
• added red lines at 0 score line for percolator
• added additional prediction step checkpoint to avoid having to predict again when starting after ce-calibration
• added workshop notebook for google collab
• changed documentation to point to koina.wilhelmlab.org
• version bump to 0.6.1

Technical details

Additional context