Strip Down Default config.xml

Go through **EVERY LINE** in [config.xml] [cfg], understand what it does, and remove it if it doesn't make sense as the default for Yokozuna.

Also, rename this file to `solrconfig.xml` as that's what it is called in the Solr example and it will cause less confusion for those users who already have experience with Solr.

[cfg]: https://github.com/rzezeski/yokozuna/blob/master/priv/conf/config.xml