TST: Adjust boxplot tests following MPL API change

fliers on a boxplot are now 1 object instead of 2.
DOC/CLN: Cleanups plotting.py
PERF: Improve performance of CustomBusinessDay
TST: compat for *.pkl -> *.pickle in pandas/tests/data
PEP8 fixups
Merge pull request #8293 from bjonen/fix_8236_2

PERF: Improve performance CustmBusinessDay - 2nd
TST: fix path for getting pickles wrt (GH8431)
Merge pull request #8429 from TomAugspurger/flier-test-adjust

TST: Adjust boxplot tests following MPL API change
PERF: optimize storage type for codes in Categoricals (GH8453)
BUG: fix applymap to handle Timedelta
Merge pull request #8459 from TomAugspurger/plot_cln

VIS: Cleanups in plotting.py
Merge pull request #8461 from jreback/applymap

BUG: fix applymap to handle Timedelta
Merge pull request #8455 from jreback/cat2

PERF: optimize storage type for codes in Categoricals (GH8453)
WIP