Warehouse over-prioritization

[Firestorm-253]

Once a warehouse is tasked with importing a certain resource, the production buildings will refuse to continue getting resources from the original source, even if the warehouse is empty or overwhelmed.

The same problem occurs when two warehouses are next to each other.
In this case only the closer one is used, even if it is empty and the other one isn't.

Also i think there should be a user option to import a ressource to a warhouse without having to select the source.