Trade update v1.20

1. Reworked part of the trade system: part 1
1.1 Each port now has an individual supply and demand.
1.2 Added production/consumption icon to the trade window based on port's production
1.3 Port's supply and demand can now be seen by clicking on the port's icon on the Map screen
1.4 Added additional trade goods.
1.5 Port's doubloons and trade goods are now saved. Preventing exploitation.
1.6 Port's doubloons and items goes incrementally back to their default values after a half in game day
1.7 Added additional trade related instructions to pirate-o-pedia
2. Ranking up again is now possible after reaching rank viceroy. Making gaining additional skill points possible
3. Fixed rare crash when save's timestamp is incorrect.