Add SIGNAL option to Getter/Setter generator (for Q_PROPERTY matching)

After implementing QTCREATORBUG-1890 the getter and setter work quite nice.

But there is the pattern of the setter emitting a signal, currently the pattern is:

void setSomething(type something) {
    m_something = something;
}

This could be easily extended to:

void setSomething(type something) {
    if (something == m_something)
        return;
    m_something = something;
    emit somethingChanged()   
}

Of course the signal somethingChanged() would be also autocreated.

This is not a reopen on QTCREATORBUG-1890, because you wont always (but very often) want to emit a signal.

Also, this fix, in conjunction with the wonderfully auto Q_PROPERTY creator already in place would make life even easier as the pattern of creating properties is very common.