Various small quality-of-life changes for gunners

[Charon]

• Allow proactive reloads. Sometimes I'm left with only a few rounds in a magazine and would like to discard it to grab another. As far as I can find, the only way to do this is by firing off the rest of the magazine.
• Add the option to nestle to the gunsight by clicking and holding, rather than as a toggle. This would be nice for those of us with thumb-buttons on our mice. This could just be an additional keybinding "Turret: nestle to gunsight (hold)".
• Decouple zoom level from scroll speed. Often I want to zoom in to ID a target, but having scroll speed change dramatically while this happens makes it hard to aim.
• When nestled to the gunsight, don't ever detach the head from the stock when hitting limits. It's better to halt the gun than have the view jump abruptly (this is especially disorienting in VR). The He 111 rear ventral gun in particular is very hard to use now because the camera so readily goes screwy.
• Add an option to hide the white targeting circle. I prefer to play with no visible UI elements.
• In campaigns, generate names for the crew and list them as casualties when appropriate, rather than having them be anonymous "redshirts".
• Where a gun position has a turret with a flexible mount (e.g. He 111), give the option to drive the turret directly and independently from pivoting the gun itself. Having them move together means that small motions are too slow (the whole turret needs to move), but large movements are too fast (the turret movement is fast seemingly to make up for the fact that it is used too frequently).