[Suggeston] Option to not encode textures to .bbmodel files

[0ffz]

Currently, textures are encoded to the model file itself. This makes sense, as packaging everything into one model file is favorable.

However, textures often need to be opened in other programs, so to bypass this, blockbench prompts users to make a copy of every texture in a file externally. This isn't inherently problematic, but there are cases where only working with external files is favorable.

For example, I would like to keep track of my models in version control, as they are just json files, while also tracking my binary image files in something like git LFS. Currently I am essentially forced to keep a copy of each texture file in my version history for every commit I make.

An option (saved in the model file itself) to only load textures from files would make collaboration much simpler, especially when combined with using relative paths (#906).

Additionally, the ability to turn this option on or off by default for new files would also be very appreciated.