[Recommendation] Modernize the code by using Qt5 signal APIs instead of Qt4's

[mhogomchungu]

Below codes looks strange in a new Qt5 only project

    connect(downloadThread, SIGNAL(started()), this, SLOT(messageDownload()));
    connect(downloadThread, SIGNAL(started()), this, SLOT(setStatusClose()));
    connect(downloadThread, SIGNAL(started()), download_instance, SLOT(download()));
    connect(download_instance, SIGNAL(returnFinished(int)), this, SLOT(setStatusClose()));
    connect(download_instance, SIGNAL(returnFinished(int)), this, SLOT(printResult(int)));

Their Qt5 equivalent is

    connect(downloadThread, &QThread::started,[this](){messageDownload();});
    connect(downloadThread, &QThread::started,[this](){setStatusClose();});
    connect(downloadThread, &QThread::started,[download_instance](){download_instance->download();});

    connect(download_instance, &mainCommand::returnFinished,[this](int){setStatusClose();});
    connect(download_instance, &mainCommand::returnFinished,[this](int s){printResult(s);});

Using lambdas and Qt5 signals may require a some refactoring but i think it will make the code a lot more pleasant to look at from strangers and it greatly improves readability sometimes when slot code is placed in a lambda itself so that its easy to see the code that will execute at a place were the connection is made.

[JaGoLi]

After working on other projects, the refactoring, improvement, and modernization of this one starts. All connect calls have been updated to qt5 in the latest beta commit.