Add default implementation for IDocument::fallbackSaveAs(Path|FileName)

The methods are only relevant for documents without a filePath, and
there was a mix of different irrelevant implementations present in
subclasses.

Change-Id: I4f57d306e5ddd913974cfe6ed0b4db062eb907a1
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>

src/plugins/modeleditor/modeldocument.cpp

@@ -106,16 +106,6 @@ bool ModelDocument::save(QString *errorString, const QString &name, bool autoSav
     return true;
 }
 
-QString ModelDocument::fallbackSaveAsPath() const
-{
-    return QLatin1String(".");
-}
-
-QString ModelDocument::fallbackSaveAsFileName() const
-{
-    return tr("model.qmodel");
-}
-
 bool ModelDocument::isModified() const
 {
     return d->documentController ? d->documentController->projectController()->isModified() : false;