In order to synchronize the Low Power mode, the services were
immediately informed about the frequency change,
so that they can update their resources (e.g. PWM filling)
and services may request the maximum CPU frequency in order
to perform a task (e.g. screen redraw, telephone conversation)
Till now there was no clear way to register hanlder for message in
Service, with this approach one can register function/lambda handler
for Message which encurages handling messages in functions rather than
in hudge switch cases.
With aproach like this our Messages resembe something between Command
and State pattern. In state pattern `Message` would be `Event` send,
whereas Service would be `Context`.
