Physical constant calculation in `World`

[laingawbl]

This is a subtask of #2 .

What?

Port the calculation of physical constants from pan-gaia. Briefly, the calculation process exposes a set of primary constants which the user can set (e.g. planetary orbit and solar temperature), and derived constants which are calculated from the primaries (e.g. solar constant).

The calculation should expose at least four methods (maybe they are in a class by themselves? maybe part of the World class?? TBD) :

• Load an entire set of primary constants from a ConfigFile of ICs
• Set the value of a single primary constant.
• Get the value of any primary or derived constant.
• Get a KV map of the entire set of primary and derived constants.

Calling the first two methods should cause recalculation of the derived parameters (as a start, you can recalculate them all; later, you might separate them into groups that can be recalculated only if the primary variables they are derived from change).

Write some sanity-checking unit tests for each derived parameter.

[laingawbl]

Idea for later: having a DAG structure of dependent values so you can visualize what is changed by changing a certain primary