Hiding the id from the Actor struct

[tisztamo]

Do not force the user to write boilerplate like

mutable struct TreeActor <: Component
    id::ComponentId
    children::Vector{ComponentId}
    TreeActor() = new(rand(ComponentId), [])
end

The ideal solution would be

mutable struct TreeActor <: Component
    children::Vector{ComponentId}
    TreeActor() = new([])
end

And also providing the alternative

@component TreeActor
    children::Vector{ComponentId}
    TreeActor() = new([])
end