(AppManager): fix auto-start services

What does this MR do?

Fixes AppManager to start automatically services when all associated objects are available.

How to test it?

In this example, myService is never started 😢

::fwData::Image::sptr myData = ::fwData::Image::New();
appmMng->addObject(myData, s_IMAGE_ID);

// this method :
// - starts all the services with autoStart=true and with all the required objects 
// - allows to start a service when adding an object later
appmMng->startServices();

// add a service in autoStart mode with a required fwData::Image in input:
const bool autoStart = true, autoUpdate = true;
auto myService = appmMng->addService("::myBundle::SService", "srvName", autoStart, autoUpdate);
myService ->registerInput(cameraTimeshift, "camera");

[UPDATE]

You can test this feature with the unit-test managerWithObjectTest in fwServiceTest:

> bin/fwservicestest fwServices::ut::AppManagerTest::managerWithObjectTest

Data

No data required

Associated issue

Closes #302 (closed)