Vcx-100 special arc

[Mu0n]

I propose adding "special arc" in the "firing arcs" key.

The main advantage for us in the X-Wing vassal crew would be to complete the upcoming feature of being able to construct on the fly any ship base (present and future) with this trait, even if it's not already in the module. It could also be constructed conditonally on having a docked attack shuttle.

[guidokessels]

I believe all VCX-100 pilots have this in their pilots.js entry:

    "grants": [
      {
        "type": "firing_arc",
        "name": "Auxiliary Rear",
        "slot": "Torpedo"
      }
    ]

I believe I did it like this to be able to specify that it only works for Torpedoes.

I'm ok with adding a special entry to ships.json, though I am a bit unsure how we'll handle it if FFG releases an other ship with a special firing arc that is different than the VCX's.

[Mu0n]

I'm not married to finding that bit of information in "arcs". I'll just detect it in the "grants" key, thanks!