Added in a new custom option for the DateTime format to allow the user to input their own format

src/core/lib/DateTime.mjs

@@ -15,6 +15,10 @@ export const UNITS = ["Seconds (s)", "Milliseconds (ms)", "Microseconds (μs)",
  * DateTime formats.
  */
 export const DATETIME_FORMATS = [
+    {
+        name: "Custom",
+        value: ""
+    },
     {
         name: "Standard date and time",
         value: "DD/MM/YYYY HH:mm:ss"