Implement ical feed for contingents

composer.json

@@ -20,7 +20,9 @@
     "georgringer/news": "^7.2",
     "gridelementsteam/gridelements": "^9.2",
     "helhum/typo3-console": "^5.6",
+    "kigkonsult/icalcreator": "^2.29",
     "league/csv": "^9.2",
+    "league/period": "^4.9",
     "pixelant/pxa-social-feed": "^2.0",
     "symfony/http-client": "^4.3",
     "symfony/options-resolver": "^4.2",