Add user agent to all headers

[fronzbot]

Description:

• Add user agent to all headers

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 #361 into dev will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev     #361   +/-   ##
=======================================
  Coverage   83.07%   83.07%           
=======================================
  Files           8        8           
  Lines         951      951           
=======================================
  Hits          790      790           
  Misses        161      161           

Flag	Coverage Δ
#unittests	83.07% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
blinkpy/auth.py	94.90% <100.00%> (ø)

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