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/CatchRunner.h

@@ -0,0 +1,14 @@
+#ifndef FSFW_TESTS_USER_UNITTEST_CORE_CATCHRUNNER_H_
+#define FSFW_TESTS_USER_UNITTEST_CORE_CATCHRUNNER_H_
+
+namespace fsfwtest {
+
+/**
+ * Can be called by upper level main() if default Catch2 main is overriden
+ * @return
+ */
+int customMain(int argc, char* argv[]);
+
+}
+
+#endif /* FSFW_TESTS_USER_UNITTEST_CORE_CATCHRUNNER_H_ */