WT: Add Key Done so that you can display the key in the hole

[illyaine]

MontyTRC89/TombEngine#1408

I would also like to see a “Key Done” slot.
Then you can build the key hole so that the key is inside at the end. Then the whole thing looks more real.
Because let's be honest, when Lara uses the key, where is it? At the moment it just disappears and looks strange.

I have already posted this on “TombEngine”. But since it is also about the WADTool, I think it should also be posted here :)