Show effective cost for objects given a certain year

[LeftofZen]

It could be useful to show in the editor the 'real' cost of building that object, given a certain year in the game. This would be shown on the UI as a real cost calculated from cost index and cost factor, and would need some kind of input for the in-game date, which would then set the inflation table which is also required for the calculation.

see: https://github.com/OpenLoco/OpenLoco/blob/master/src/OpenLoco/src/Economy/Economy.cpp#L130-L136