add resource buffer to building costs to keep resources for upkeep costs

[Daxtorim]

It's a little annoying when you queue up a few Helium-3 Collectors and anytime one gets build all the starports shut down because all the Helium-3 went towards completing structures rather than paying upkeep, just for the starports to come back online the very next game loop. Wouldn't be a problem if you didn't need to reassign all the craftsmen again, but alas...

I made this an option since it applies to all resources and takes into account crafting and trading as well. If you have a lot of trade routes active this could add several thousands to building costs (not the actual costs, just the affordability check).

[yarukishi]

The game currently has logic to intentionally allow structures and technologies to be purchased with a negative one second buffer, so adding a positive buffer to a negative buffer may not be the best implementation.