Feat: View + Manage Pipeline (#53)

This MR adds the `.pipeline()` command which opens up the pipeline popup. This popup shows information about the current pipeline and it's jobs, and gives users the ability to re-trigger failed jobs.

cmd/approve.go

@@ -11,6 +11,7 @@ func ApproveHandler(w http.ResponseWriter, r *http.Request) {
 	c := r.Context().Value("client").(Client)
 
 	if r.Method != http.MethodPost {
+		w.Header().Set("Allow", http.MethodPost)
 		c.handleError(w, errors.New("Invalid request type"), "That request type is not allowed", http.StatusMethodNotAllowed)
 		return
 	}