Issue description
Currently, maintenance reductions are additive rather than multiplicative, which makes the Statue of Maintenance and Maintenance Reducer edicts behave oddly at non-Captain difficulties. If you set the game difficulty's modifier negative (i.e. easier), the edicts are stronger than expected, whereas higher difficulty settings make the edicts weaker than expected.
Expected behavior
Expected behavior from turning on both Maintenance Reducer edicts should be a reduction of either 25% or 23.5% from where you were prior to turning the edicts on.
However, on Sailor difficulty, what one gets is actually a 41% reduction.
I would expect a building requiring 1.0 maintenance/min at unmodified Captain to behave like one of these two scenarios
0.6 (Sailor difficulty) * 0.75 (both edicts) = 0.45
0.6 (Sailor difficulty) * 0.85 (edict I) * 0.9 (edict II) = 0.459
However, what is actually encountered in-game is this:
1 - 0.4 (Sailor difficulty) - 0.25 (both edicts) = 0.35
This isn't 25% less than your 0.6 baseline, it's 41% less. The same effect is observed with the Statue of Maintenance, albeit on a smaller scale.
On the flipside, Admiral difficulty would weaken the effect of the edicts, as you're subtracting a constant amount from a higher baseline.
Reproduction steps
Turn on Maintenance Reducer edicts (and/or build the Statue of Maintenance) at different game difficulty settings.
Game version
0.4.11
