WIP: Device layer port to nRF52840

[emargolis]

-- Test Travis script changes.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (feature/nrf52840-device-layer-local@8e460d2). Click here to learn what that means.
The diff coverage is n/a.

@@                          Coverage Diff                           @@
##             feature/nrf52840-device-layer-local       #4   +/-   ##
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  Coverage                                       ?   53.59%           
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  Files                                          ?      326           
  Lines                                          ?    55461           
  Branches                                       ?        0           
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  Hits                                           ?    29726           
  Misses                                         ?    25735           
  Partials                                       ?        0

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