Fix #297, CCSDS Command Secondary Header Endian Agnostic

[skliper]

Describe the contribution
Implement CCSDS command secondary header such that it is endian agnostic in code and unit test support.
Fix #297

Testing performed
Steps taken to test the contribution:

1. Tested via bundle CI (including non-zero command send to reset)
2. Also tested locally with enabling TO via cFS-GroundSystem

This covered both direct cmdUtil call and cFS-GroundSystem use.

Expected behavior changes
Cmd code (and checksum) are always in the same place (matches GSFC spec for command secondary header)

System(s) tested on

• Hardware: CI and cFS Dev Server
• OS: Ubuntu 18.04
• Versions: test bundle with this change and Fix #65, CCSDS Command Secondary Header Endian Agnostic cFS-GroundSystem#66 in cFS-GroundStation

Additional context
See also nasa/cFS-GroundSystem#66 these should be merged together

Third party code
None

Contributor Info - All information REQUIRED for consideration of pull request
Jacob Hageman - NASA/GSFC

[skliper]

@BaldBeacon @tngo67 - ping.

*EDIT - tagged wrong person.

[astrogeco]

CCB 2020-04-01 - Discussed. Will break systems that are little endian as happened in a previous cFE version. Users who need this functionality can apply the diff. APPROVED