Replace FANCY_AO constant with user-configurable value

[bunabyt3]

This is a fairly simple change. Some users may not like the look of 50%-visible ambient occlusion. and will wish to change it to align more closely with what they remember from older versions of Minecraft. It might be somewhat helpful to move this option into the "Nostalgia" screen, since its main purpose is to more closely approximate the behaviour of old versions of Minecraft, and so it may be easier for users to find it there, maybe even merged with a more obvious setting. I think this is good enough for now though.

[Goodlyay]

Some thoughts on this

I think the option button should be renamed to "Corner shading" or something more descriptive than AO, since many people will not understand this term.

I don't think the option belongs in nostalgia screen.

1. Minecraft has never to my knowledge featured AO control beyond smooth lighting on/off, which is already in graphics options
2. This option is contingent on two other options in the graphics screen, and moving it would only make that more confusing

Ideally this option should be grayed out until you turn both smooth lighting and fancy lighting on. There probably needs to be a way to display option descriptions even when grayed out. This would be useful for the lighting mode when it's locked too.

[bunabyt3]

Minecraft has never to my knowledge featured AO control beyond smooth lighting on/off, which is already in graphics options

@Goodlyay you're correct. However, Minecraft's AO is (or used to be) pitch black, rather than the 50% intensity that ClassiCube is hardcoded to use (more intense AO looks better in my opinion, but not for everyone, which is why I made it optional). Optifine, a popular Minecraft mod, even includes a dedicated setting to change the intensity of AO, indicating that user control over this value is a desirable feature in Minecraft and similar games.

I'm also working to fix some of your UI and UX concerns, but I'm glad to take suggestions.

[bunabyt3]

Closing this because it's had no activity in a while. It's just waiting to cause conflicts with other, more important contributions.