Submissions by pi_pi3 tagged fixes

As the title says, a lot of different stuff today. I'll just make a list of new features for an easy overview.

- JSON based cuboids creating (see pic below)

- New blocks: dirt and grass

- New textures for stone bricks and rock (no 4 shades of green anymore)

- Support for multi-textured blocks (different textures for sides, top and bottom)

- Thanks to the JSON cuboids, easy cuboid creation

- Fixed an annoying texture bug which caused the textures to shift by .5 meters

- Fixed collision when jumping (it was previously possible to jump into the ceiling)