Applications should use all-inclusive "cfe.h" header

[jphickey]

Is your feature request related to a problem? Please describe.
The CFE documentation recommends that applications use the supplied cfe.h header which in turn provides all CFE core, PSP, and OSAL APIs as well as mission config.

Because some header names are getting changed in nasa/cFE#1203, including the headers individually becomes a problem.

Describe the solution you'd like
Change to using the cfe.h all-inclusive header, which makes ci_lab work with the new directory structure, and should avoid future issues, and it matches what the documentation recommends.

Describe alternatives you've considered
Change cfe_msg_api.h -> cfe_msg.h

Additional context
Needed for nasa/cFE#1203

Requester Info
Joseph Hickey, Vantage Systems, Inc.