- Removing Catch2 code from codebase, will pull it via FetchContent instead.

- Changing StdOutLogger to OStreamLogger, so that test cases output can be silenced.

tests/main.cpp

@@ -3,7 +3,8 @@
 #include "daggy/DAG.hpp"
 
 #define CATCH_CONFIG_MAIN
-#include "catch.hpp"
+
+#include <catch2/catch.hpp>
 
 TEST_CASE("Sanity tests", "[sanity]") {
     REQUIRE(1 == 1);