More work to support nullable foreign keys

Adds nullable int/uint types

backend/internal/util/time.go

@@ -0,0 +1,9 @@
+package util
+
+import "time"
+
+// UnixMilliToNiceFormat converts a millisecond to nice string
+func UnixMilliToNiceFormat(milli int64) string {
+	t := time.Unix(0, milli*int64(time.Millisecond))
+	return t.Format("2006-01-02 15:04:05")
+}