Show proposition of changes in diff-like format

[Grigorij-Dudnik]

We need to improve printing for replace_code tool to improve readability. Instad of just printing new code to insert and lines where it should be inserted, better print both old and new code (diff format).

The most intuitive way to print it will to place old code on the left side, and new on the right; althrough I'm not sure if cmd will provide enough space to place both code files in one horizontal level. Make experiments to figure it out. If not, solution will be printing first old code and then new one.