Make FSFW tests accessible from outside

1. Further reduces the amount of code the user needs to copy and paste
2. Makes FSFW tests more accessible. This can be used to simplify moving mission unit tests
   to the FSFW
3. A lot of include improvements

tests/src/fsfw_tests/unit/printChar.cpp

@@ -0,0 +1,10 @@
+#include "printChar.h"
+#include <cstdio>
+
+void printChar(const char* character, bool errStream) {
+	if(errStream) {
+		std::putc(*character, stderr);
+		return;
+	}
+	std::putc(*character, stdout);
+}