1.8/14w08a terrain.png update

requires updated materials.py and minecraft.yaml
Merge pull request #484
Submodule pymclevel updated.

Submodule pymclevel:
    > ebfd1ed - pocket.yaml: Fix indent in #32 and #253, auto-cleanup
    > 45fe0e9 - Added blocks, fixed wooden slab
    > 82334bc - Missing blocks are pink again
    > 29b901c - Update to allow greater than 16x16 in terrain.png
    > 17e5033 - 1.8/14w08a minecraft.yml update