alias tree: add pgp signature status, adapt colors

gitconfig

@@ -21,4 +21,4 @@
 
 [alias]
 	s = status --short --untracked-files=all --branch
-	tree = log --graph --abbrev-commit --decorate --format=format:'%C(red)%h%C(reset)%C(bold red)%d%C(reset) %C(dim green)(%ar)%C(reset) %C(dim white)%s%C(reset) %C(bold black)(%an, %ai)%C(reset)' --all --date=short
+	tree = log --graph --format=format:'%C(red)%G?%C(reset) %C(yellow)%h%C(reset)%C(blue)%d%C(reset) %C(dim green)%ar%C(reset) %C(white)%s%C(reset) %C(dim black)(%an, %ai)%C(reset)' --all