Modernize client code (#6250)

* Various code style fixes
* Use range based for loops
* Use empty instead of empty objects
* Use C++11 default keyword for trivial constructors and destructors
* Drop some useless casts
* Use emplace_back instead of push_back to improve performance of some vectors push

src/client/clientlauncher.h

@@ -29,7 +29,7 @@ class RenderingEngine;
 class ClientLauncher
 {
 public:
-	ClientLauncher() {}
+	ClientLauncher() = default;
 
 	~ClientLauncher();