Refactor

[znotfireman]

Implements the following framework:

ext:newCommand({
    id = "rename-selection",
    title = "Rename Selection",
    description = "Renames the current selection to the given pattern.",
}, function(ctx)
    return {
        renderViewport = function()
            -- ...
        end
    }
end)

This is again very destructive, so I'm waiting on the Arc Parts command to be PR'ed.