Adding modpack support

[Maelstromeous]

Was speaking to @tehruttiger privately about this, I think it would be a good idea to create the ability for users to choose between a number of popular modpacks out of the box to enable very quick onboarding for such users.

One popular icon modpack is https://sentsu.itch.io/foxhole-ui-label-icons.

I've attached a zip of what I've got so far, I'm painfully collecting them all as and when I see new items, but currently limited by Tech, and currently only able to do it for the wardens (thankfully I can move to collies on another shard).

UI changes

In terms of UI, I recommend you add a dropdown picker to enable users to choose which modpack they wish to use, which we supply the modpack icons out of the box.

Filesystem changes

Convert /CheckImages/Modded into /CheckImages/Modded/Custom and create new folders under the Modded folder, e.g. /CheckImages/Moddded/FoxholeUiLabelIcons, and insert the collected icons into that.

Example filestructure:

Stockpiler/
├─ CheckImages/
│  ├─ Modded/
│  │  ├─ Custom/
│  │  ├─ FoxholeUiLabels/
│  │  ├─ SomeOtherMod/

Then when users choose 'Custom' (being the default option) it will assign itself to the correct folder.