Utils: Rework aspect implementation

This avoids some repetition and could be a step towards
having type storage in (or rather accessible from) the base,
so we can have aspects for more complex data (treemodels...)
that are not easily converted to QVariant.

Change-Id: I9797b3d5646195705212db1830d2b415291ac651
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/git/gitplugin.cpp

@@ -1466,9 +1466,8 @@ void GitPluginPrivate::setupInstantBlame()
         forceInstantBlame();
     };
 
-    connect(&settings().instantBlame, &BoolAspect::valueChanged, this,
-            [this, setupBlameForEditor](bool enabled) {
-        if (enabled)
+    connect(&settings().instantBlame, &BaseAspect::changed, this, [this, setupBlameForEditor] {
+        if (settings().instantBlame())
             setupBlameForEditor(EditorManager::currentEditor());
         else
             stopInstantBlame();