Version 2.16 - bug fixes, and Ender Chest

[Eric, just a guy]

I added a faked-up Ender Chest and fixed some bugs with display and
color schemes.

Full note:
bug fixes: fixed 3D printing color export for Sculpteo (OBJ) format
viewed in SAP Viewer, fixed output of relative texture coordinates for
OBJ export. Fixed color schemes so that old color schemes will
autoupdate when used with newer worlds.Provided guidance to Mac users
looking for their world directory (still trying to figure out how to
make this happen automatically). Added Xzip/unzip in anticipation of
someday reading texture packs directly for textures. Added Ender
Chest, but only for default terrain.png. Thanks to Sterling Babcock
for bug reports and the Ender Chest texture addition.

Eric