Add a size->height mapping
whitespace
Change nominal height of Huge base models

Nominal height for huge bases is defined in Warmachine: Colossals it
turns out, and is exactly 5".
Whitespace
Implement damage grids via composition

As the comment explains, recognize that damage grids can be represented
on the basis of composition and hack out the standard damage grid forms
on that basis. This will need some work to support repairs, shield regen
and other effects, but that can be done.
Add tests for the Box types
Whitespace
Rename the shield field from :n to :shield
Remove FIXME for adding damage grids