Final 1.8 update terrain.png

Added a few more missing textures, and updated a few textures courtesy
of OniOniOn
Merge pull request #488
Pocket: New terrain.png
Submodule pymclevel updated.

Submodule pymclevel:
    > 8bf7b3d - Pocket: Fixed water, sandstone, quartz textures
    > 0039447 - Syntax Fixes
    > daea425 - Final 0.8.0 pocket.yaml update
    > b3ddbb8 - Final 1.8 Minecraft.yaml Update