Convert Messages to TypeScript

(cherry picked from commit 0fdeb0566305311dcec344074b5de9e38b8d8090)

frontend/src/App/State/MessagesAppState.ts

@@ -0,0 +1,15 @@
+import ModelBase from 'App/ModelBase';
+import AppSectionState from 'App/State/AppSectionState';
+
+export type MessageType = 'error' | 'info' | 'success' | 'warning';
+
+export interface Message extends ModelBase {
+  hideAfter: number;
+  message: string;
+  name: string;
+  type: MessageType;
+}
+
+type MessagesAppState = AppSectionState<Message>;
+
+export default MessagesAppState;