implement full chat room function

build.gradle

...otlin/de/thk/gm/websocketsdemo/configs/WebSocketConfig.kt

.../thk/gm/websocketsdemo/controllers/ChatRoomsController.kt

src/main/kotlin/de/thk/gm/websocketsdemo/dtos/ChatRoomDto.kt

...lin/de/thk/gm/websocketsdemo/handlers/ChatRoomsHandler.kt

src/main/kotlin/de/thk/gm/websocketsdemo/models/ChatRoom.kt

...thk/gm/websocketsdemo/repositories/ChatRoomsRepository.kt

...lin/de/thk/gm/websocketsdemo/services/ChatRoomsService.kt

...de/thk/gm/websocketsdemo/services/ChatRoomsServiceImpl.kt

src/main/resources/templates/chatRooms/showChatRoom.ftlh

src/main/resources/templates/chatRooms/showChatRooms.ftlh

src/main/resources/templates/index.ftlh