allow File::name to be queried using 'name' property

This would allow the following ways to query `br::File::name`:

    br::File myFile = ...;
    QString myFileName = myFile.get<QString>("name"); // Equivalent to myFile.name;

and

    br::TemplateList myTemplates = ...;
    QStringList myFileNames = br::File::get<QString>(myTemplates, "name"); // No current equivalent