I/O - ports on Storages

Change I/O - ports on storages to what we have with balancers.
That way we either could toggle the direction of storage buildings (maybe if it was empty first) or use 1 import and 3 export. This gives more flexibility to storages.

Very good idea. Very useful if you want to reverse the direction of a connection to feed a consuming building, instead of stocking the resource. Simply reverse the transport and the port.