Added: Buttons

Added buttons. They are placed and updated properly.

Tested and well. :)
@turt2live I took example from @jkcclemens in https://github.com/JeromSar/Glowstone/commit/8d9cf2febb247e0bbf011ca6f5faa92f1aaf244b#diff-53a5eb7d2e87a87b269421a3e89446a8R20

Seemed odd but I went with it.