Wing display name

[MjnMixael]

Adds Display name for wings. Fixes #1730 (the last request from that ticket).

Wing display name takes priority over ship display name in all cases. Works for the initial wing and all following waves.

There's a lot of baggage and edge cases with ship display names. I deliberately wanted to avoid all of that. Since this is a new feature, no mods can have used it yet so we can be reasonably sure that if wing display name is parsed then that's the display name we want to use. I'm sure there are plenty of edge cases and tweaks that will come up as mods start picking up the feature but for now this solves what BtA really needs and gets wing display name on the bus. We can refine it as mods make requests later. This simple feature allows, finally, translating wing names without hacks.

[naomimyselfandi]

Lgtm. Mjn described his test plan to me on Discord; it included the first and second waves of a wing with display names, the first and second waves of a wing without display names as a regression test, and save/load round trips in both FRED and QtFred. We also discussed the decision to let wing display names override ship display names. Arguably, a ship display name "should" override a wing display name, but it introduces legitimate ambiguity around how waves after the first should be handled; in light of the historical baggage around ship display names, we agreed that simplicity was preferable. (ship-change-display-name remains an option for special cases, with or without a wing display name.)