Refactor C++ version of the Gilded Rose kata

* Make it possible to build and run tests in CLion
  and Visual Studio 2019 out of the box

* Provide four types of initial test using different test frameworks:
  * Catch2 test framework
    * Traditional unit testing using Catch2
    * Approval test using Catch2
  * Google Test test framework
    * Traditional unit testing using Google Test
    * Approval test using Google Test

* The different types of initial test are located in separate folders
  in the test folder.

* Remove scripts to build and run tests and replace
  with instructions in the cpp README.md

* Use C++17

* Use CMake => 3.13

cpp/.gitignore

@@ -1,4 +1,4 @@
 .idea
+.vs
 cmake-build-debug
-gtest
 build