[client] added new input:mouseRedraw option

This new option, when enabled (the default) enables cursor movements to
trigger frame updates in the client, improving responsiveness at the
cost of increased FPS while the mouse is moving around.

client/src/main.h

@@ -160,6 +160,7 @@ struct AppParams
 
   const char * windowTitle;
   int          mouseSens;
+  bool         mouseRedraw;
 };
 
 struct CBRequest