City details panels could use some more hover information

**Issue by [vttale](https://github.com/vttale)**
_Tuesday Jan 10, 2017 at 17:12 GMT_
_Originally opened as https://github.com/CQUI-Org/cqui/issues/241_

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The city details panel has all this info about citizen growth but without much explanation, and of course Civpedia is useless for explaining it.

Like, I've got one city like this, currently @ pop 39:

- Food per turn: +98
- Food consumption: -78
- Growth food per turn: +20 (difference of prior two lines)
- Amenities growth bonus: -15% (which is clear from the subpanel below it)
- Other growth bonuses: +40%
- Modified food per turn: +25 (Growth food * (1 + (Amenities bonus + Other bonus))
- Housing multiplier: 1 (from Housing subpanel, Population growth rate normal)
- Occupied City multiplier: N/A
- Total Food Surplus +25

My main issues here are not seeing how base "Food per turn" is calculated or what "Other growth bonuses" are. I'm guessing the +98 value includes both worked tile production and any trade routes, as well as the granary and water mill, and a tooltip would clarify that.

As for Other growth bonuses, I'm stumped. I don't have any policies that do that, or wonders. (Is there a list of wonders you have somewhere? This game started in the last era though so I definitely don't have Hanging Gardens.) I'm Suzerain for two city-states, neither of which produces growth. What is this 40% coming from?

No files or tests are named. Locate the city details panel implementation and inspect how the growth values are assembled and displayed, along with any existing hover information. The work is done when the relevant food and growth bonus values have clear hover explanations, including their sources or calculations.

Written by the indexing model from the issue text.