Monitor a Great Person

**Issue by [vttale](https://github.com/vttale)**
_Friday Dec 23, 2016 at 21:14 GMT_
_Originally opened as https://github.com/CQUI-Org/cqui/issues/189_

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Sometimes I see a Great Person that I really want to get and it either looks like I am on track to earning them normally or could possibly opt to get them through patronage. Then the next time I look, the GP is gone, apparently sniped by the patronage or city project of some other civ and I'm left scratching my head about when that happened and if I could have somehow prempted it.

What'd be really great is if I could tap a Great Person of Interest, and get notified if I can afford it via patronage or if another civ is threatening to overtake my earning it via normal GPPPT (obviously have to exclude their patronage or city projects).

The issue names no files, tests, or entry points to start from. First identify where Great Person progress, patronage, and city-project data are exposed in the mod, then define how a tracked person and the resulting notifications should be represented and tested.

Written by the indexing model from the issue text.