added prefix scan and fixed logout issue

pkg/store/helper.go

@@ -0,0 +1,11 @@
+// Copyright (C) 2019 Marius Schellenberger
+
+package store
+
+// Parts taken from strings.TrimPrefix
+func hasTrimPrefix(s, prefix string) (string, bool) {
+	if len(s) >= len(prefix) && s[0:len(prefix)] == prefix {
+		return s[len(prefix):], true
+	}
+	return s, false
+}