fix:#5 added room table and changed sql query

frontend/src/api/requestFreeRooms.ts

@@ -0,0 +1,16 @@
+
+
+// load free rooms as a list of strings form the backend
+
+export async function requestFreeRooms(from: string, to: string): Promise<string[]> {
+  console.debug("requestFreeRooms: from=" + from + ", to=" + to)
+  const rooms: string[] = [];
+  await fetch("/api/rooms/free?from=" + from + "&to=" + to)
+    .then((response) => {
+      return response.json();
+    })
+    .then((roomsResponse: [] | null) => {
+      roomsResponse?.forEach((room: string) => rooms.push(room));
+    });
+  return rooms;
+}