Display spillover production in Production Panel

**Issue by [vttale](https://github.com/vttale)**
_Friday Nov 18, 2016 at 01:44 GMT_
_Originally opened as https://github.com/CQUI-Org/cqui/issues/110_

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Could the number of spillover hammers you have after completing a project be displayed in the top box? Like, right now I'm looking at my city screen after having overproduced on a builder and not only does it say "Art museum completed" because of that other bug with showing the previous thing made, it also has a pretty useless "0/265" below it which would be a whole lot more useful if it were instead "42 excess {cog}" or such.

Start at the Production Panel UI entry point and reproduce the case by overproducing a builder project. Confirm what the top box currently displays after completion, then make the spillover production visible as excess hammers and verify the completed-project display remains correct.

Written by the indexing model from the issue text.