Add no purge, manual delete options (#12)

- Add htmx, hx attributes
- Only add/update items since last check
- Move messages to session to persist across redirects
- Polish styles a bit (still WIP)

src/app-config.php

@@ -15,3 +15,6 @@ spl_autoload_register(function ($class) {
 require 'user-config.php';
 
 Data::ensureDb();
+
+/** @var string The date the world wide web was created */
+const WWW_EPOCH = '1993-04-30T00:00:00+00:00';