Enforce keywords for most args and rearrange signatures

[mwaskom]

Making good on the warning added in v0.11.0, plotting functions now require explicit keywords for most of their arguments.

Additionally, signatures have been arranged to place data first, as the only non-keyword argument. Now all functions have a consistent signature

func(data, *, [x, y,], [hue,], ...)

Aside from consistency, this reorganizatino has a couple advantages:

• With wide-form data handling, (nearly) all functions will do something when called as func(data)
• Pandas dataframes can be directly piped into all seaborn functions without writing (func, "data").

On the keyword-only side of the signature, a few functions were further reorganized to group together releated parameters that had been added at different times.

For more context, see the original function that added the warning: #2081

Fixes #2055

[codecov]

Codecov Report

Merging #2804 (c63ec16) into master (bb03ae1) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2804      +/-   ##
==========================================
- Coverage   97.47%   97.45%   -0.03%     
==========================================
  Files          17       17              
  Lines        6451     6399      -52     
==========================================
- Hits         6288     6236      -52     
  Misses        163      163              

Impacted Files	Coverage Δ
seaborn/axisgrid.py	96.05% <ø> (-0.03%)	⬇️
seaborn/categorical.py	98.24% <ø> (-0.02%)	⬇️
seaborn/matrix.py	95.81% <ø> (-0.04%)	⬇️
seaborn/regression.py	97.85% <ø> (-0.03%)	⬇️
seaborn/_decorators.py	100.00% <100.00%> (ø)
seaborn/distributions.py	96.38% <100.00%> (-0.02%)	⬇️
seaborn/relational.py	99.69% <100.00%> (-0.01%)	⬇️

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