Reworked tree splitting.

Moved the logic from the axe to the tree library for better handling.
Also, dual splitting with two players is effective now (hasn't been before).
Added Chunk_Wood.

Reworked all trees to split into Chunk_Wood.
Basic buildings are now constructed from Chunk_Wood.

These are:
- Flagpole (until we get another power distributor)
- Foundry
- Sawmill
- Tools Workshop
- Wind Generator
Fixed tree splitting wood output.
Added planks- Get some them from the sawmill.

Reworked quite a lot of production costs to either planks or chunk_wood. Haven't done a thourough search. I expact that soon Chunk_Wood is renamed into Wood anyway, so any errors will solve themselves.