[layer23] Cleanup of mobile application

[layer23] Cleanup of mobile application

All functions for handling mobile instances and mobile relevant parts are
moved to mobile/app_mobile.c, the mobile/main.c and mobile/mncc.c become a
simple out-of-the-box mobile application. (making calls)

The mobile/main.c can be replaced easily by a different application now.
this application may have it's own call control implementation (layer 4).
Full configurations via VTY is still possible and required in this case.