Implement project Essential_L12.2 (Events - WPF - Calculator)
Update gitignore
Improved project Essential_L12.2
Add classes Calculator.cs, OperationRequest.cs, OperationResponse.cs and enumerator Operations.cs
Improved project Essential_L12.2
Merge pull request #38 from anna-kulyk/L12.2

Implement project Essential_L12.2 (Events - WPF - Calculator)