WT: Add an option to copy single textures pieces for legacy objects

[LoreRaider]

WadTool way of handling textures for legacy objects makes it easy to bloat up .wad2 file, because the whole texture page is copied even if a little texture is used by the object.

This easily makes Tomb Editor to overflow its textures buffer, causing this issue to happen:

https://github.com/MontyTRC89/Tomb-Editor/assets/48493527/ac9dd74b-e2fc-4f9b-b268-89cfd448ba5f

To prevent this, there could be an option in Tools->Options... that allows copying texture pieces instead of the whole texture pages, so that it's less likely to bloat up .wad2 and so to not overflow Tomb Editor texture buffer.