#244 Colopedia: Add texts for the "chapters" as well

[Wuzzy]

In the Colopedia, the various "chapters" (e.g. "Terrain Types", "Bonus Resources", "Goods", "Units", "Founding Fathers", "Concepts", "Nations", etc.) don't have a text associated with them if you have selected them. So if you select e.g. Founding Fathers directly in the Colopedia (not one of the sub-entries in the tree), you see an empty page.

I suggest to add at least a brief introduction to every "chapter" to explain what it is about. And maybe more useful explanations for the more complex stuff like Founding Fathers.

(Note that the Founding Father nomination window currently has a help button which puts you in the Colopedia at "Founding Father" chapter, so the player is currently linked to an empty page.)