Notifications for when GPs are claimed

**Issue by [vttale](https://github.com/vttale)**
_Friday Dec 23, 2016 at 21:11 GMT_
_Originally opened as https://github.com/CQUI-Org/cqui/issues/188_

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Could we get a notification when another civ claims a Great Person? I see at the end of the game that the information is available for what civs took which people and when, but don't know if it is while a game is in progress.

The issue names no files, tests, or entry points. Start by locating the existing end-of-game information about which civilizations claimed Great People and when, then trace whether that data is available during play. Done means players receive a notification when another civilization claims a Great Person.

Written by the indexing model from the issue text.