Fix #80, cmd and tlm messages use payload sub-structure

[havencarlson]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution
Fix #80, adds Payload substructure to all command and telemetry messages

Testing performed
unit testing

Expected behavior changes
no impact to behavior

System(s) tested on

• OS: Ubuntu 18.04

Contributor Info - All information REQUIRED for consideration of pull request
Haven Carlson - NASA