Update data/generator/sfPropelModule/admin15/template/lib/helper.php

Fixed module generator Helper template.

Now it uses `params['moduleName']` instead of `params['route_prefix']` for url generation.
`url_for` supports `module/action` instead of route name to generate url.

All was fine when `route_prefix` was equal to `moduleName`. But in other cases we've got an error while generating url for *moveUp* and *moveDown* actions.