Added the first skeleton code for PieceGenerator.

This is a WIP and won't work / isn't used at all.
Added Vector3i::Move().
Added BlockFaceToString() translation function.
PieceGenerator can connect two connectors of the same type.

Also added extensive debugging output and a test.
Merge branch 'master' into PieceGenerator
Merge branch 'master' into PieceGenerator
cPieceGenerator: New connectors are added to the free pool.
Added cCuboid::Engulf().
ChunkDef: Replaced enums with static const ints.

This makes them easier to use in std::min et al.
Hardened cCuboid with asserts for its assumptions.
A working POCPiece generator.
POCPieces: Added height.

Now the pieces connect in different heights, too, creating a true 3D maze.
Removed debugging output.

Kept it commented-out for later revisions, if needed.
Merge pull request #791 from mc-server/PieceGenerator

Piece generator