ProjectExplorer: Use FilePath for ProjectNode::{path,directory}

... and let the fallout trickle down a bit.

Change-Id: I1a2f79e281725c4a121cc2fbbc0377e881616ce5
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/coreplugin/icore.cpp

@@ -245,7 +245,7 @@ ICore::~ICore()
 */
 void ICore::showNewItemDialog(const QString &title,
                               const QList<IWizardFactory *> &factories,
-                              const QString &defaultLocation,
+                              const FilePath &defaultLocation,
                               const QVariantMap &extraVariables)
 {
     QTC_ASSERT(!isNewItemDialogRunning(), return);