Customizable strings

**What do you want to see?**
All strings used in the game should be customizable in one or more data files. (This would be a good place to use the include feature that I think we added to data files a while back!)

**How would it help players?**
This would allow for localization of the game and customization of the UI (see #36).

**Alternatives**
N/A

**Screenshots and mockups**
SE5 handles this in an OK fashion, but we don't need to localize data file field names themselves (e.g. Number of Abilities => Numero del los Abilidades or whatever), that just leads to mod incompatibility!

**Things to consider**
We need to distinguish between strings that should be persistent across multiple mods and strings that belong to a single mod. We could put those in separate data files to make it easier to override only the moddable ones and not the standard ones. For instance, you might want a mod to rename "bases" to "capital ships" (remember the failed Capship Mod?)

We could also if we want define "terminology anchors" (I use these at work) which are standardized strings that can be replaced on a mod level with a customized string following certain grammatical rules. For instance, [S|Base] might resolve to "Base" or "Capital Ship" or whatever, while [SL|Base] would be "base" / "capital ship" and [P|Base] would be Bases or Capital Ships, and [SLA|Base] would be "a base" or "a capital ship"... maybe [G|Base] could be "Base's"? G for Genitive since P for Possessive would conflict with Plural... [TL|Base] could be "the base" since some languages have different definite articles for different words (e.g. gendered "le/la" in French) - no Anthony if you are reading this, I am not going to steal any of your code :) just might reuse the idea of the terminology anchors you have!