Cleanup equip strings

This is the second part of #3294, so it must be merged first.

### First commit

If the flight mode is called "Manual Control", I guess it should be "Autopilot Control" when in Autopilot, either way: don't reuse the equipment string, for indicating the flight mode.

### Second commit

I think pioneer cheated by reusing equipment strings for showing equipment mounts. Now we can have "Atmospheric __s__ hielding yes/no" and "Atmospheric __S__ hielding" for the equipment, which is consistent with how we write equipment, and their respective slots.

### Third commit

This might be the controversial one, and I'm only arguing for it if, as I remember @robn (ping!) saying, that transifex allows moving of strings, so no re-translation should be needed. I hope my memory of him saying that is right.

So, my arguments for moving equipment strings from core to its own module are:

1. `core` is for C++ / `src/` strings.

2. It is easier for translators when each module/file to translate is used in a specific context. Like equipment market, and mission `lang/module-`s.

3. Conversely, translating `core` strings is very difficult since the strings are just piled on top of each other and often you have no idea where the strings are used. Example: `HAT` (is not worn on the head), `JOY` (is not an emotion), `X`, (is not an in game coordinate nor location, but a `JOY`stick axis).

4. `core` is a behemoth and overwhelmingly long, possibly being intimidating for a translator to start working on.

__Question:__ I don't know if the name of the new module should be `equipment-core`? Once the rest of the UI is in lua, also the commodities aught to be moved out from core, but into the same `equipment-core` module, or into another one?