Feature: Ability to see unknown/modded blocks as missing texture blocks

[cubebotfan]

This suggestion is a downgrade of #43
I'm using this extension with structures that contain modded blocks and all the modded blocks are completely invisible.
I wasn't expecting full functionality but was hoping there would at least be something to display the unknown blocks.

It would be nice if instead of having unknown blocks be completely invisible, they could be shown as opaque missing texture blocks that you can click to see their block names and nbt so that you can still get a general idea of what the structure looks like.

[Dryhb]

In a similar sense, be able to support old naming system (pre 1.13 minecraft). For example, slime block is named "slime_block" 1.13+ but only "slime" pre 1.13, which makes it not render.
Same issue with glass & others where the system pre 1.13 was stained_glass to "_stained_glass" 1.13+.
Does not make sens to have both types in the same file (pre 1.13 and 1.13+) but have a way to toggle between naming convention would be really helpful.
Could 'simply' be a mapping from old name to new name and add that conversion step if required.
Otherwise awesome tool !