some housekeeping

[mdeff]

For some reason, I felt the need to clean up my stuff a bit.

• [x] Merge dangling branches: wikipedia (4bf213d), plot-filters (49431c1), long-standing (742ff46). The code is left as is (unfinished) for reference.
• [x] put all experiments (mnist, 20news, rcv1, wikipedia) in one folder (f731393)
• [x] fill in versions in requirements.txt (f7f7ba1)
• [ ] add environment.yml as an alternative (specify python, good for binder)
• [ ] store all notebook outputs in the outputs branch
• [ ] test binder and add a link?
• [ ] notebook header
• [ ] readme: add link to poster
• [ ] readme: code organization