Add reporter to get plain list of files

Use this if you want to open all files in your favorite editor. This
formatter outputs just the names of the files and makes it possible to
do something like: `scss-lint -f Files | xargs vim`

Change-Id: I64f17d14dab54a735882135484e66ab521b62a18
Reviewed-on: https://gerrit.causes.com/32723
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>