Introduce Utils::TreeView/TreeWidget

The only view that is sane is my view. Adds handling of return/enter
for macintosh. Allows for overriding whether single or double click
activates items via setActivationMode.

Change-Id: Id8f9001f99162833c682dfc5b2b1abac04ce18a3
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/coreplugin/manhattanstyle.cpp

@@ -360,6 +360,13 @@ int ManhattanStyle::styleHint(StyleHint hint, const QStyleOption *option, const
     case QStyle::SH_ItemView_ArrowKeysNavigateIntoChildren:
         ret = true;
         break;
+    case QStyle::SH_ItemView_ActivateItemOnSingleClick:
+        // default depends on the style
+        if (widget) {
+            QVariant activationMode = widget->property("ActivationMode");
+            if (activationMode.isValid())
+                ret = activationMode.toBool();
+        }
     default:
         break;
     }