Output folder name for stats files

[Faizal-Eeman]

    @Faizal-Eeman I think the case for `call-gSV` and `call-sSV` should be different. I think most of those `Stats` files are the summary of the Manta calling results: https://github.com/Illumina/manta/blob/master/docs/userGuide/README.md#statistics

I am okay with the current version, we can wait for @tyamaguchi-ucla to decide when he comes back.

Originally posted by @maotian06 in #74 (comment)