WIP changes after rebuttal

[jolars]

Checklist for camera-ready paper

• [x] Clarify introduction (common misconceptions)
• [x] Specify coordinate-wise separability
• [x] Add reference for SLOPE prox
• [x] Add motivation for choice of standardization
• [x] Clarify what density means in tables
• [x] Clarify y axes in figures 6 and 7
• [ ] Mention per-iteration complexity
• [x] Modify abstract regarding "overclaim about improvement"
• [x] Use alternative interval notation in remark 2.1
• [x] Reiterate v = 5
• [x] Add path results to paper (and add acknowledgement to LUNARC for these experiments)

[jolars]

Note that we have an additional page now for the camera-ready version, so we have a bit of space if we want to include something in the main paper. I'm thinking maybe the partial smoothness proposition and/or the path benchmarks, and/or iteration-complexity, and/or extensions to other datafits.