Fix db relations, add sample data, show categories in frontend menu

software/backend/models/order.model.ts

@@ -0,0 +1,21 @@
+import { Table, Column, Model, BelongsTo, ForeignKey, HasMany, BelongsToMany } from 'sequelize-typescript';
+import { Account } from './account.model';
+import { OrderedItem } from './orderedItem.model';
+import { Product } from './product.model';
+
+@Table
+export class Order extends Model {
+  @Column
+  @ForeignKey(() => Account)
+  accountId: number
+
+  @Column
+  totalPrice: number
+
+  // Relations
+  @BelongsTo(() => Account)
+  user: Account
+
+  @BelongsToMany(() => Product, () => OrderedItem)
+  orderedItems: OrderedItem
+}