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/test/cpp_catch2_unittest/GildedRoseCatch2UnitTests.cc

@@ -0,0 +1,12 @@
+#define CATCH_CONFIG_MAIN  // This tells Catch to provide a main() - only do this in one cpp file
+#include "Catch.hpp"
+#include "GildedRose.h"
+
+TEST_CASE("GildedRoseUnitTest", "Foo")
+{
+    vector<Item> items;
+    items.push_back(Item("Foo", 0, 0));
+    GildedRose app(items);
+    app.updateQuality();
+    REQUIRE("fixme" == app.items[0].name);
+}