Changes required to make minecarts work.

[mklingen]

• [x] Change the state representation in A star planner to one which includes info about the minecart state.
• [x] Change MoveAction so that it goes from an abstract state to another abstract state rather than voxel to voxel.
• [x] Query minecart rails in planner to determine whether the dwarf can ride them.
• [x] Add MoveActions for getting on and off minecarts and riding a minecart.
• [x] Add animations for getting on and off minecarts, and riding minecarts.
• [x] Create minecart entity.
• [x] Implement for multi-voxel rails.
• [x] implement path planning with correct rail topology.
• [x] create new minecart sprites
• [x] make building rails easier.
• [x] balance resource consumption of rails.

[mklingen]

this feature is almost done. There are still several loose ends with the artwork and balance/UX. In particular it needs to be easier to build and destroy rails.