Player selection of avatar / character model

[Cervator]

The player should be able to select / customize their default avatar representation in the main menu somewhere. I'm considering this issue's main purpose being able to choose an avatar, we have an older GSOC level item for deeper customization: #2239

This could easily be overridden in particular gameplay settings, like for instance in Light & Shadow the player may end up choosing in-game on a spawn platform where they pick a side/role via NPC dialogue. But we should provide a way to pick your default avatar used when no override is in place.

Three primary options come to mind:

• Add a new option under the Player Settings, where you also configure your name and such. This has the drawback that no modules are loaded while in the main menu at the moment. As a cheap proof of concept this could be done with a model temporarily stored in the engine
• Tie into a new preview stage for creating/joining a game. @msteiger had started on this with #2074 but that code needs more work and some dusting off. The concept is loading up a module environment without creating the world yet, letting the player configure various details with the appropriate modules loaded - this has all kinds of potential benefits, including being able to easily scan for available models within the given module selection
• Integrate with an online model/skin repository. This would be like how you with Minecraft (and maybe MineTest? Dunno) would set your skin at the account level. Different technical challenges with the benefit of being able to load assets away from the game rather than worry about modules. Main drawback is that we don't have an online user account concept at all.

Ultimately the user would ideally be presented with a preview of their chosen avatar (a simple drop-down would suffice for early proof of concept). #1532 heavily relates to that and could also lead to in-game options for customization. Other than potentially applying the chosen player color to clothing I'm not too worried about customizing art assets while in the main menu just yet, that can come later via #1532 and #2239

Over time we might achieve all the listed options one after the other. A base set of models (maybe even a simple one in the engine, at least temporarily) with an option to find skins for them online. We may even want to consider support for reusing MC/MT skins (poking @kaen) - should we cave and make the more classic voxelated humanoid available? Or maybe get clever with an alternative model that would just so happen to fit the same skins? There could be a few model options paired with each their own pool of skins.

We naturally also need some actual artwork for player avatar candidates. @glasz has a few options found in the forum. We might want some more options, or even adopt some existing free artwork. We also need to support animation for PCs (#2475) and maybe support previewing said animations.

The scope on this item could vary wildly based on the target we pick, could be mentor sized or even GSOC sized (really, we might want to just merge those labels)

[Cervator]

Customize avatar

Note that since this issue was created we've added https://github.com/Terasology/HumanoidCharacters/ which now has both a female (default) and male (extra) model included. In some game modes like L&S you'd start with an alternative default like the Fool. Also note that as of me writing this we just converted to glTF from md5 and said two models aren't fully hooked up right, there's an item for fixing that as part of #4156