Cities next to Ponds Shouldn't Build Navies

[QuintillusCFC]

In Civ, there's a minimum size, I think it's 21, for lakes to support navies. This should probably be configurable, as sometimes it would be nice to do a stealth invasion across a small lake.

But right now, the C7 AI just looks at the presence of a coast:

That navy is never going to be useful; Croton should be building something else.

Marking as a bug but also as low-priority since this is a rare and not super consequential occurrence. You can still fix it if you want though.

[WildWeazel]

This will be referenced for a few things: "coastal" production options, "fresh water" proximity, and the food yield (is that a hard coded +1 for freshwater coast?). I think any sea or ocean tiles automatically mean it's considered open sea.

[QuintillusCFC]

Good questions. I just wrote #368 to cover those questions. I also gave it a new label that we can hopefully use to make it easy for non-coders to find areas where they can contribute.