Add a {{date}} tag for wiki forms, a=chris

diff --git a/src/library/WikiParser.php b/src/library/WikiParser.php
index fd0fdd69b..35c2f9248 100644
--- a/src/library/WikiParser.php
+++ b/src/library/WikiParser.php
@@ -192,7 +192,10 @@ class WikiParser implements CrawlConstants
         ];
         $braces_substitutions = [
             ["/{{timestamp}}/si",
-                "<input type='hidden' name='username' value='" .time(). "' />"],
+                "<input type='hidden' name='timestamp' value='" .time()."' />"],
+            ["/{{date}}/si",
+                "<input type='hidden' name='timestamp' value='" .date('r').
+                "' />"],
             ["/{{username}}/si",
                 "<input type='hidden' name='username' value='[{username}]' />"],
             ["/{{image-captcha\|(.+?)}}/si", "<div class='csv-captcha'>".