Production queue - change BuildTimeSpeedUpDivisor

This is needed. The current integer parameter was limited - we could never have less than a 50% build speed reduction.

I `grep`ed for mods using this yaml setting and found none.

*EDIT: Changed how this works.*
- Follows an exponential decay for build times, rather than linear, so a 36 second build time unit will jump from 36->30->26 with 15% decay over three steps (total of three production buildings).
- The total amount of steps is already configurable.