Reduce code complexity with rails useful helpers.

The intention of the seeds directory is that will be
only stored yaml files. With rails helpers we can
reduce the yaml extesion checker and assume that
files always will be right.
Change Repository.loa type argument to String.

Since it is in our control, we can pass String and
avoid unecessary Symbol->String convertion.
Convert symbol stored data to string.

The stored yaml data should be simple. Not worry about
symbols.