Change Calculator for Creative Cash Draw Solutions

[HalJordan409]

This PR implements the change calculator as outlined in the Cash Register problem.

Features:

• Built using .NET Core 3.1
• Provides a GUI built in Avalonia that allows the user to select a file to parse and outputs the contents of the file along with the calculated change
• Isolated the Cash Register logic into a class library so that it can be easily extracted and used in a larger system
• The GetChange function will return the minimum amount of change, except when the amount due to the clerk is divisible by 3
• If the amount due to the clerk is divisible by 3, the change denominations returned to the customer will be randomized

Other notes:

• I had fun using/learning Avalonia. I could've easily built a SPA + REST API that uploaded a file, but chose to learn a new technology.
• I also had a good experience using Rider. I only have a Mac and it's nice to know that if I wanted to return to C#/.NET Core development, Rider is a great option.
• Areas for improvement:
  • Acceptance/integration tests for Desktop project
  • Better UI experience
  • Validation for input file integrity
  • Save output to it's own file