Make option ID editable and allow copying of other node IDs

[RailKill]

Feature Request

• Node ID should have a click-to-copy button
• Option ID should be editable and also have a click-to-copy button
• After clicking on click-to-copy, there should be feedback saying "Copied!" on the screen; right now there is no feedback when click-to-copy option IDs

[RailKill]

Copy buttons have been added beside ID LineEdit for nodes and options. The copy icon is from the Godot Engine (ActionCopy.svg). Clicking on the copy button will now show a ribbon notification saying "Copied!" which will disappear in 1 second, so the user knows that they've copied the ID to clipboard.

[RailKill]

Previously, IDs are only checked between graph nodes, but not options nodes. Because option IDs are now editable, it needs to be checked to ensure it is unique throughout all types of nodes. dfe48ef fixes this critical bug by checking all nodes to prevent identical IDs from being input by the user.