Document what script variables are usable in which data file fields

**What do you want to see?**
A wiki page that shows a list of all variables that are accessible in each data file's fields. For instance, maybe in Components.txt you have access to a hull and an empire or whatever.

**How would it help players?**
Make modding so much easier!

**Alternatives**
Instead of one wiki page for all the script variables, each data file's wiki page could get its own list.

**Screenshots and mockups**
In components.txt you can access:
* hull - the hull of the vehicle to which the component is being added. Of type IHull with the following properties: blah blah blah
* empire - the empire to which the design belongs. Of type Empire with the following properties: blah blah blah

**Things to consider**
N/A