More scalastyle work; addresses #196.

[ruebot]

GitHub issue(s): #196

What does this Pull Request do?

More scalastyle work; addresses #196.

• Remove all underscore imports, except shapeless
• Address all scalastyle warnings
• Update scalastyle config for magic numbers, and null (only used in
  tests)

How should this be tested?

TravisCI

Additional Notes:

The shapeless imports in TupleFormatter are a little hairy. I'll loop back around to them sometime in the future.

[codecov]

Codecov Report

Merging #339 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #339   +/-   ##
=======================================
  Coverage   74.95%   74.95%           
=======================================
  Files          39       39           
  Lines        1122     1122           
  Branches      197      197           
=======================================
  Hits          841      841           
  Misses        214      214           
  Partials       67       67

Impacted Files	Coverage Δ
...c/main/scala/io/archivesunleashed/df/package.scala	95.23% <ø> (ø)	⬆️
...scala/io/archivesunleashed/app/WriteGraphXML.scala	100% <ø> (ø)	⬆️
...scala/io/archivesunleashed/app/ExtractGraphX.scala	92.1% <ø> (ø)	⬆️
...in/scala/io/archivesunleashed/app/WriteGraph.scala	98.38% <ø> (ø)	⬆️
.../scala/io/archivesunleashed/app/WriteGraphML.scala	100% <ø> (ø)	⬆️
...ala/io/archivesunleashed/app/NERCombinedJson.scala	0% <ø> (ø)	⬆️
...ala/io/archivesunleashed/app/ExtractEntities.scala	0% <ø> (ø)	⬆️
...ain/scala/io/archivesunleashed/app/WriteGEXF.scala	100% <ø> (ø)	⬆️
...la/io/archivesunleashed/matchbox/ExtractDate.scala	72.22% <ø> (ø)	⬆️
...n/scala/io/archivesunleashed/DataFrameLoader.scala	100% <ø> (ø)	⬆️
... and 3 more

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[ianmilligan1]

Looks great (and kicked the tires locally and all checks out)!