Expose the entry file name & path in vars

It's the next part of https://github.com/farazdagi/phrozn/pull/55 now the layout have also the info

> This pull request put in this.vars the name of the current entry.
> 
> in entries/index.twig :
> {{ this.phr_template }}
> will be tranformed to
> index.twig
> 
> in entries/dir/index.twig :
> {{ this.phr_template }}
> will be tranformed to
> dir/index.twig

in layout you can access to phr_template by using
{{ current_page.phr_template }}