Extend database with more tables, rewrite API doc, improve API endpoints

software/backend/models/category.model.ts

@@ -1,7 +1,7 @@
 import { Table, Column, Model, BelongsTo, ForeignKey, HasMany, Unique } from 'sequelize-typescript';
 import { Product } from './product.model';
 
-@Table
+@Table({ timestamps: false })
 export class Category extends Model {
   @Unique
   @Column