Fix relative ids when copying to clipboard and skip null relative ids when pasting

[ivan-morandi-zupit]

• When copying, the relative id is initialized but never removed, thus when making multiple copy paste, the relative ids may match with multiple nodes. I removed the relative ids and used a local map to store the relative ids.
• When pasting, the origin_node was not set to null correctly as the var scope is the entire function. As the scope is the entire function, if the relative id of the origin node is null, the origin node may had the previous value, which then creates links between nodes that never existed before.