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/inputhandler.cpp

@@ -102,8 +102,7 @@ bool MyEventReceiver::OnEvent(const SEvent &event)
 		};
 		assert(event.LogEvent.Level < ARRLEN(irr_loglev_conv));
 		g_logger.log(irr_loglev_conv[event.LogEvent.Level],
-				std::string("Irrlicht: ") +
-						(const char *)event.LogEvent.Text);
+				std::string("Irrlicht: ") + event.LogEvent.Text);
 		return true;
 	}
 	/* always return false in order to continue processing events */