Decompose GameState into sub-records

[kostmo]

Towards #872

Previously, the GameState record had 41 toplevel members. It now has 22. Logical grouping of the fields makes it easier to peruse the code and paves the way to split State.hs into smaller modules. Some functions now may even be able to operate exclusively on subsets of the game state, rather than having to pass in GameState as a whole.

There is potential to go even farther, by extracting view-related and robot-related members to their own records, but I figured I'd pursue this refactoring incrementally.

[byorgey]

This is great! It's a good idea in general, and I like the subcategories you have chosen to organize things. There are just two improvements I'd like to see:

• New subrecord types like Temporal, Landscape, etc. should be exported (just the types, not their constructors or record fields)
• We should put some effort into organizing the generated Haddock documentation. At the very least we should put each of the new subrecords + their lenses under a separate subheading in the export list.