Improved texture organization

It's totally fine if this doesn't get added, I understand you're very busy and are doing a lot of other stuff. (Also, I couldn't find a way to report anything but bugs on the issue tracker, that's why I'm here).

Basically, I think it would be neat to see better texture organization in the files. Currently, if you crack it open, it's just blocks, items, and a zillion random other textures. I think that it could be improved, perhaps with stuff like mob_effect, entity, gui, etc. This would clean it up a bit, and make it much easier for people to navigate the assets of mods.