Add Lua global variables library

[MjnMixael]

Adds a new library for access global variables and defines.

I wanted max ship primary and secondary banks and couldn't decide if that should go in base, ui, tables, or somewhere else. Having it accessible as part of ShipClasses wasn't great because you'd need to access it as part of an existing ship class.

I also wanted access to a couple other global defines and so I decided a global variables library made sense. I could take or leave it if there's a better place to put these, though, as this is purely an organizational question. Actual code access to these values is trivial... they just needed a home.