Adding a global error message

This error message should be used for non fatal errors (otherwise, use the ErrorScene).
It is implemented using Svelte and the new "$errorStore".

Use `errorStore.addErrorMessage` to display the error popup with the message.

This PR uses this error message to display a popup explaining the browser is too old for WebRTC.

front/src/Stores/Errors/BrowserTooOldError.ts

@@ -0,0 +1,8 @@
+export class BrowserTooOldError extends Error {
+    static NAME = 'BrowserTooOldError';
+
+    constructor() {
+        super('Unable to access your camera or microphone. Your browser is too old. Please consider upgrading your browser or try using a recent version of Chrome.');
+        this.name = BrowserTooOldError.NAME;
+    }
+}