[Original #1295] v2 dcd format and tests

[avtolstoy]

Correctly rebased

Original #1295

Problem

Hypothesised write errors in flash that appear only after power cycle can corrupt the configuration data.
Flash access is not thread-safe.

Solution

Adds CRC checking to the Electron DCD implementation so that write errors are detected.
Add a critical section around flash operations and around DCD operations.

Steps to Test

Run the firmware unit tests.

Manual testing:

• flash system firmware to an electron that was connecting to the cloud
• verify that the device continues to connect to the cloud
• make a change in DCD via DFU
• verify the device still connects to the cloud (the DCD contents will have been upgraded to the V2 format.)

Example App

This is an internal system change. No example application.

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation (N/A)
• Added to CHANGELOG.md after merging (add links to docs and issues)

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Enhancement

• [PR #1330] [Electron] Added CRC checking to the Electron DCD implementation so that write errors are detected. Added a critical section around flash operations and around DCD operations to make them thread safe.

[technobly]

Previously approved by Andrey