save auth key

[mkmer]

Description:

Small bit of cleanup on the blinksync application: add back save .json key, exit when username is blank or auth fails, lint/black minor changes

Related issue (if applicable): fixes #

Checklist:

• Local tests with tox run successfully PR cannot be meged unless tests pass
• Changes tested locally to ensure platform still works as intended
• Tests added to verify new code works

[codecov]

Codecov Report

Merging #737 (1779a73) into dev (50b395d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev     #737   +/-   ##
=======================================
  Coverage   99.64%   99.64%           
=======================================
  Files           8        8           
  Lines        1394     1394           
=======================================
  Hits         1389     1389           
  Misses          5        5           

Flag	Coverage Δ
unittests	99.64% <ø> (ø)

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