Initialise global message

- Create new class to manager global message. My idea is that this class permit to manage audio or text message.
 - Update html to have main content id and inject html in this.
 - Create front event to receive startMessage and stopMessage.
 - Delete impoted variable not used.

front/src/WebRtc/GlobalMessageManager.ts

@@ -0,0 +1,43 @@
+import {HtmlUtils} from "./HtmlUtils";
+import {Connection, GlobalMessageInterface} from "../Connection";
+
+export class GlobalMessageManager {
+
+    private Connection: Connection;
+
+    constructor(Connection: Connection) {
+        this.Connection = Connection;
+        this.initialise();
+    }
+
+    initialise(){
+        //receive signal to show message
+        this.Connection.receivePlayGlobalMessage((message: GlobalMessageInterface) => {
+            this.playMessage(message.id, message.message);
+        });
+
+        //receive signal to close message
+        this.Connection.receiveStopGlobalMessage((message: GlobalMessageInterface) => {
+            this.stopMessage(message.id);
+        });
+    }
+
+    playMessage(messageId : number, htmlMessage: string){
+        const div = document.createElement('div');
+        div.innerHTML = htmlMessage;
+        div.id = this.getHtmlMessageId(messageId);
+        div.className = "message-container";
+
+        const mainSectionDiv = HtmlUtils.getElementByIdOrFail<HTMLDivElement>('main-container');
+        mainSectionDiv.appendChild(div);
+    }
+
+    stopMessage(messageId: number){
+        HtmlUtils.removeElementByIdOrFail<HTMLDivElement>(this.getHtmlMessageId(messageId));
+    }
+
+    private getHtmlMessageId(messageId: number){
+        return `message-${messageId}`;
+    }
+
+}