Apps should use CFE_MSG_PTR macro instead of cast or local unwrapping

[skliper]

Apps typically cast to a CFE_MSG_Message_t or use *.Msg. Better to use abstracted CFE_MSG_PTR. NOTE - Not backwards compatible with Caelum so recommend not addressing in Draco.

Imported from GSFCCFS-1900

[skliper]

Fixed in #58, recommend closure