Change whitelist/blacklist to allowlist/denylist

[tzm41]

This PR fixes #63 by updating the naming of MAC filter keywords in accordance with other OpenThread projects.

The PRs openthread/pyspinel#100, openthread/openthread#5507, and openthread/wpantund#474 updated the naming of whitelist/blacklist to allowlist/denylist to promote inclusivity and eliminate any unintentional bias. We update Silk to adapt to the latest wpantund changes.

[codecov-commenter]

Codecov Report

Merging #64 into master will not change coverage.
The diff coverage is 20.00%.

@@           Coverage Diff           @@
##           master      #64   +/-   ##
=======================================
  Coverage   41.72%   41.72%           
=======================================
  Files          37       37           
  Lines        3851     3851           
=======================================
  Hits         1607     1607           
  Misses       2244     2244           

Impacted Files	Coverage Δ
silk/config/config.py	0.00% <0.00%> (ø)
silk/node/wpantund_base.py	27.55% <40.00%> (ø)
silk/config/wpan_constants.py	100.00% <100.00%> (ø)

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[priyankaCh22]

LGTM

[qilinkang]

LGTM