Outstanding categorical work

[mwaskom]

• [x] Fix the data object attached to the FacetGrid returned from catplot (#3494)
• [x] Add a log_scale parameter (#3445)
• [ ] Reduce some of the redundancy in the *plot function bodies (e.g. setting the categorical scale)
• [x] Improve the legend artist to reflect fill and ideally other kwargs (#3467)
• [ ] Update the catplot unit tests
• [x] Change "gray" special edgecolor value to "auto" (#3460)
• [ ] Sync default kwargs between catplot and axes-level functions better by inspecting signatures?

[mwaskom]

The open items are internal cleanup and can be postponed to v0.13.1 to accelerate release.