ofono: implement basic functionality for the wan service functionality

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>
ofono: implementation of the VoiceCallManager and VoiceCall interfaces

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>
telephony: implementation of the first bits of the call control API

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>
ofono: telephony: send a power status notification whenever power status changes

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>
Don't check for service state in every API method call

When an API method is called the serivce ensures that the underlaying service layer is
fully initialized. If the backend isn't initialized yet it's part of the corresponding
plugin to report this through the error object structure.

This is really important as otherwise subscriptions by clients in early lifetime of the
daemon aren't processed and get lost.

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>
Defer ls2 service registration until backend is ready

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>
ofono: free all used memory when shutting down

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>
ofono: if service disappears correctly provide this information to upper layers

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>
wan: extended service interface to support set API method

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>
ofono: wan: implement set API method

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>
ofono: initial support for voice call management

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>