Add untracked command in order to check for untracked files

[joseluisq]

It would be great if we can add support for untracked files checking on the working tree.

The way to do it, it's to use git clean with --dry-run which just check untracked files. -d is used for directories checking as well.

git clean --dry-run -d

Proposal: I suggest introduce an untracked command in order to perform this operation.

~> untracked
Would remove a
Would remove abc/
Would remove b
Would remove c