Refined domain model; eliminated long parameter list in Format.

1. Got rid off AssemblyCost;
2. Renamed Name as Number;
3. Cleaned up Bom using list comprehensions;
4. Reanmed BomPart as Node;
5. Cost API -- introduced times() and deleted _add_to()
6. Quantity -- cost() now invokes cost.times()
7. Related Changes in Configuration and test;
8. New design that eliminates long parameter list in Format.