Fix vanilla issue: Production panel shows incorrect completion time for wonders if there are multiple bonuses

**Issue by [bolbass](https://github.com/bolbass)**
_Saturday Jun 24, 2017 at 06:52 GMT_
_Originally opened as https://github.com/CQUI-Org/cqui/issues/563_

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When a player has 2 bonuses to wonder production, Production panel uses only one of them to calculate turns to complete values. See more on [civfanatics](https://forums.civfanatics.com/threads/cqui-a-ui-overhaul-now-out-on-steam-workshop.602771/page-32#post-14795306).

Start by reproducing the issue in the Production panel with two wonder-production bonuses, using the linked CivFanatics example for context. Trace how the panel calculates turns to completion for wonders; done means the displayed completion time accounts for all applicable bonuses.

Written by the indexing model from the issue text.