Mineways 12.08: 1.21.6 dried ghast added, and small fixes

[Eric Haines]

Mineways 12.08: 1.21.6 dried ghast added, and small fixes.

• Added 1.21.6 blocks, i.e., the dried ghast.
• Avoid bad states between various export modes when exporting. Toggling "Export lesser, detailed blocks" put fatten and simplify mesh into meaningless states. The whole system could use a redo, but this fix should avoid some bad combinations.
• For material counting, change to a resizeable list, as the number of materials can get extremely high under certain circumstances (including individual block export).
• Fixed (more or less) for USD export multiple materials output with the same name, when exporting using the three-texture option. Warn user away from using this option with USD export. See issue #146 for more details. (Thanks to zNight for reporting this bug.)