Fixing various issues that appeared in Mac

Fixing flat qualifier in shader
Fix default values
Disable postFX shader

src/engine/openspaceengine.cpp

@@ -148,6 +148,13 @@ bool OpenSpaceEngine::create(
 	LDEBUG("Initialize FileSystem");
 	ghoul::filesystem::FileSystem::initialize();
 
+#ifdef __APPLE__
+    ghoul::filesystem::File app(argv[0]);
+    std::string dirName = app.directoryName();
+    LINFO("Setting starting directory to '" << dirName << "'");
+    FileSys.setCurrentDirectory(dirName);
+#endif
+
 	// Sanity check of values
 	if (argc < 1 || argv == nullptr) {
 		LFATAL("No arguments were passed to this function");