Move interface definition files to "inc" location

[chillfig]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I reviewed the README file to see if the feature is in the major future work.
• I performed a cursory search to see if the feature request is relevant, not redundant, nor in conflict with other tickets.

Is your feature request related to a problem? Please describe.
The interface definition files of all open source apps currently exist in the "src" directory.

Describe the solution you'd like
Create an "inc" dir to go with the "src" dir. Move the interface definitions into this location: "_msg.h", "_msgdefs.h", "_tbldefs.h", and "_events.h". Consider moving header files in both "platform_inc" and "mission_inc" to "inc"

Describe alternatives you've considered
Leaving as is.

Additional context
N/A

Requester Info
Justin Figueroa, Vantage Systems