Fix Kalender-Page for multiple rooms

src/main/resources/db/migration/V0003__room.sql

@@ -7,4 +7,4 @@ alter table users add column room_id bigint references room;
 alter table kalendertag add column room_id bigint references room;
 
 alter table kalendertag drop constraint kalendertag_day_key;
-
+alter table kalendertag add constraint kalendertag_day_room_unique unique(day,room_id);