move ipc message structure to header file

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
add information message support

The information message is supposed to tell why and when last state
change happen.  The when is always present, but reason why the change
happen depends on user co-operation.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>