Pregnancy cleanup and postpartum consistency fixes

1. Automatically normalize pregnancy variables during WombFlush and WombCleanYYFetuses
2. When normalizing empty wombs, reset pregSource even if it's negative
3. Add TerminatePregnancy utility function to terminate a pregnancy with the appropriate postpartum length, etc
4. Rework a whole bunch of places where pregnancy is terminated to use the appropriate functions and not set pregType/pregWeek/etc directly
5. Add short postpartum delay when pregnancy is completely terminated by individually removing the last ovum from pregnancy inspection

Fixes #1270 (closed)