Notification system enhanced

- Base for notifcation center
- Show text in map if no data is available

backend/models/notifications/notification.interface.ts

@@ -0,0 +1,18 @@
+import { Document } from "mongoose";
+import { IUser } from "../user/user.interface";
+
+export enum ISeverity {
+    INFO = 0,
+    SUCCESS = 1,
+    WARN = 2,
+    ERROR = 3
+}
+
+export type NotificationType = 'beat' | 'phone_alive' | 'phone_dead' | 'phone_register' | 'panic';
+
+export interface INotification extends Document {
+    type: NotificationType;
+    severity: ISeverity;
+    message: any;
+    user: IUser;
+}