Add alias for git stash --include-untracked

[salcode]

@michealengland pointed out that git stash --include-untracked

would be more convenient with an alias (though we can shorten it to git stash -u, however I don't like this shortened version because it reminds me of git add -u, which is the opposite of git stash -u in that it ONLY affects tracked files 🙄 )

Perhaps we could call it git pokemonstash (Gotta stash'em all) with

pokemonstash = stash --include-untracked

I thought git stashall might be a more traditional alternative but git stash --all already exists which does something else, so this would be confusing.

This option is only valid for push and save commands.

All ignored and untracked files are also stashed and then cleaned up with git clean.