Add the Humble Object design pattern

> The Humble Object pattern is a design pattern that was originally identified as a way to help unit testers to separate behaviors that are hard to test from behaviors that are easy to test. The idea is very simple: Split the behaviors into two modules or classes. One of those modules is humble; it contains all the hard-to-test behaviors stripped down to their barest essence. The other module contains all the testable behaviors that were stripped out of the humble object.

Described in the "Clean Architecture - A Craftsman's Guide to Software Structure and Design" 2008 book by Robert C. Martin (Uncle Bob) in the chapter 23 - "Presenters and Humble Objects"