Utils: Make AspectContainer a QObject

... and add a 'void applied()' signal.

I actually wanted to avoid that, but it seems to be a recurring
pattern of usage to do something on top of plain apply for all
children, like triggering IVersionControl::configurationChanged
in the VCS plugins.

Change-Id: Ib64c3147c6ba30b178237e51a3a377a291c550f2
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/docker/dockersettings.h

@@ -33,7 +33,7 @@
 namespace Docker {
 namespace Internal {
 
-class DockerSettings : public QObject, public Utils::AspectContainer
+class DockerSettings : public Utils::AspectContainer
 {
 public:
     DockerSettings();

src/plugins/qmakeprojectmanager/qmakesettings.h

@@ -32,7 +32,7 @@
 namespace QmakeProjectManager {
 namespace Internal {
 
-class QmakeSettings : public QObject, public Utils::AspectContainer
+class QmakeSettings : public Utils::AspectContainer
 {
     Q_OBJECT