Updating default settings so players can have a better experience.

Some changes that improve the game experience, reduce connecting time and make client have better FPS.
#63	settings->setDefault("always_fly_fast", "false") // Makes the experience of placing and taking nodes much better when flying. I find it much better to fly fast when and if you want by holding the "fast" key down.

#84 	settings->setDefault("viewing_range_nodes_max", "200"); // 240 may be too taxing on GPUs and theres no real gain in view distance.
#85	settings->setDefault("viewing_range_nodes_min", "30"); // Lots of players have rally low end GPUs, maybe most of the minetest players, the number here could be even lower.

#94 	settings->setDefault("client_unload_unused_data_timeout", "300"); // Again, most minetest players have low end GPUs and computers, maybe with limited amount of RAM, reducing the timeout for unloading unused data from 10 minutes to 5 is a good idea.

#112 	settings->setDefault("fall_bobbing_amount", "0.6"); // This makes falling much more realistic and "enjoyable".

#133 	settings->setDefault("preload_item_visuals", "false"); // I have never found any truly good reason to preload all item visuals, it just makes connecting time at least twice as long. Possible gameplay losses are minimal.

#141 	settings->setDefault("curl_timeout", "4000"); // One more setting to reduce a little the connecting time. One second may looks like little, but in real world gameplay it means a lot. Could be reduced to three seconds actually.