Start making stuff private
Move stats stuff to statistics module
Simplify restrictions code
Simplify error handling for missing cols
Avoid errors in stats when data missing
Increase default total weight for restrictions

When no total weight restriction is set, the default is 100g. When
per ingredient weight restrictions apply, increase the default to
MAXINT so that the ingredient limit is reached.
Per ingredient restrictions for repeats

When an ingredient repeats in an ingredient list, per ingredient weight
restrictions ought to restrict the *total* weight for that ingredient.

Previously the restriction applied to each occurance which is less useful.
Sample input: short crust pastry