Coding rules:

1. module implementation can include the export head files of associated runtime

2. app manager only call access the module implementation through the interface API

3. module implementation can call the app manager API from following files:
   - util.c
   - message.c
   
4. platform API: To define it   
   
5. Any platform dependent implementation of app manager should be implemented in the 
   platform specific source file, such as app_mgr_zephyr.c   

