Apply hexagonal architecture

This commit applies hexagonal architecture to our app. We have two adapters that can we can share between multiple functions and the main business logic that is easier to test.

There are comments in the code. Please take a look at them for more details about the implementation. There are no tests in this version. We'll add unit tests in the next commit.

Unit tests for the initial sample app

This version adds unit tests. They are not the best unit tests ever, but the standard tests with many mocks, similar to what we see in many applications. The test file contains detailed comments for everything we did.

The sample app code without hexagonal architecture and test

This commit represents a sample application without hexagonal architecture and tests.