Failure to get mod preview image no longer causes crash

Modding: Added 'upon adopting [belief]' trigger, allowed belief adoption to trigger uniques

Added turn number to victory replay

Clicking locally-added mods no longer crashes

By SomeTroglodyte:
- Fix off-by-one error in autoAssignPopulation
- Happiness change from bought buildings can reapply citizen focus
- Local and jpg mod previews
- Fix UnitTable layout