Adding DefaultCamera to Spatial3D view

[jviereck]

At the moment it is not possible to set the camera position and view in the Spatial3D view. This PR implements this.

[jviereck]

This PR needs to be rebased against the current main branch.

Please let me know what you mean about the overall shape of the changes. If they are good, I will rebase against main.

[jviereck]

@Wumpf thank you for taking a look at this PR and your comments.

I agree with all your comments. I left a comment on why I've introduced the view_eye_default field. Hope this is clear.

If you manage to do so, I would appreciate if you can finish this up.

[Wumpf]

putting this on draft for now until I resurrect it (hopefully later this week, maybe early next)

[Wumpf]

Obsolete now - camera in 0.27 is fully configurable by blueprint