Rework new marker and option GUI's

New marker dialog can now be accessed by pressing 'Insert' while in
game.
Option GUI now built on top of GuiSlot so that option list can be
scrolled.
Fixed saved zoom level changing when player logs in to the nether.
Fix rendering when changing zoom levels

When changing zoom levels or regions don't draw the map texture if it is
not properly loaded.

Remove debugging messages and some unused imports.
Fix GUI not closing after teleport.

Fixed regenerate regions not working properly due to closing regions but
not removing them from the region hash map.