Add cancel snooze

- Add common request validation function

src/public/request/cancel-snooze.php

@@ -0,0 +1,15 @@
+<?php declare(strict_types=1);
+
+use MyPrayerJournal\{Layout, Table, UI};
+use BitBadger\PDODocument\RemoveFields;
+
+require '../../../start.php';
+
+$req = validate_request($_GET['id'], ['GET'], false);
+
+RemoveFields::byId(Table::REQUEST, $req->id, ['snoozedUntil']);
+
+// TODO: message
+Layout::bareHead();
+UI::requestItem($req);
+Layout::bareFoot();