Setup ical4j caching class

Needed since 3.0

Signed-off-by: Álvaro Brey <alvaro.brey@nextcloud.com>

app/src/main/resources/ical4j.properties

@@ -0,0 +1,2 @@
+# suppress inspection "UnusedProperty"
+net.fortuna.ical4j.timezone.cache.impl=net.fortuna.ical4j.util.MapTimeZoneCache