hswaw/checkinator: convert timestamp to browsers timezone

Change-Id: Ib7439269bf13de530a5f170bf231f89d815b0f3e
Reviewed-on: https://gerrit.hackerspace.pl/c/hscloud/+/1246
Reviewed-by: q3k <q3k@hackerspace.pl>
diff --git a/hswaw/checkinator/at/web.py b/hswaw/checkinator/at/web.py
index 9eb5e6a..f85aa25 100644
--- a/hswaw/checkinator/at/web.py
+++ b/hswaw/checkinator/at/web.py
@@ -1,7 +1,7 @@
 import json
 import sqlite3
 from pathlib import Path
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import NamedTuple, Iterable, Iterator, List
 from functools import wraps
 from flask import Flask, render_template, abort, g, \
@@ -112,8 +112,13 @@
     
     
     @app.template_filter('strfts')
-    def strfts(ts, format='%d/%m/%Y %H:%M'):
-        return datetime.fromtimestamp(ts).strftime(format)
+    def strfts(ts, format='%Y-%m-%d %H:%M'):
+        return datetime.utcfromtimestamp(ts).strftime(format)
+
+    @app.template_filter('utcisoformat')
+    def utcisoformat(ts):
+        return datetime.utcfromtimestamp(ts).replace(
+            tzinfo=timezone.utc).isoformat()
     
     
     @app.template_filter('wikiurl')