Add Black linting check to CI and add to test reqs

[alexgleith]

Not sure if we want to do this, but it's nice to have consistent formatting 😄

Note that this doesn't run for Python 3.5, because you can't install Black for that version of Python.

[codecov]

Codecov Report

Merging #170 (7e5fea4) into master (4d9655d) will not change coverage.
The diff coverage is 84.29%.

@@ Coverage Diff @@## master #170 +/- ##
=======================================
Coverage 84.96% 84.96% =======================================
Files 12 12 Lines 1137 1137 Branches 156 156 =======================================
Hits 966 966 Misses 152 152 Partials 19 19 

Impacted Files	Coverage Δ
aodntools/ncwriter/__init__.py	100.00% <ø> (ø)
...odntools/timeseries_products/gridded_timeseries.py	0.00% <0.00%> (ø)
setup.py	0.00% <0.00%> (ø)
aodntools/timeseries_products/common.py	89.47% <81.25%> (ø)
...eseries_products/velocity_aggregated_timeseries.py	91.85% <92.53%> (ø)
...tools/timeseries_products/aggregated_timeseries.py	95.18% <94.44%> (ø)
.../timeseries_products/velocity_hourly_timeseries.py	95.20% <95.18%> (ø)
aodntools/timeseries_products/hourly_timeseries.py	98.19% <97.67%> (ø)
aodntools/__init__.py	100.00% <100.00%> (ø)
aodntools/ncwriter/imos_template.py	100.00% <100.00%> (ø)
... and 2 more

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