Add populateMenu method to MoreActionsMenu

This allows me to build the menu when the “More” button is clicked.
Polymorphic with ViewInputFilesMenu, LabelMenu, etc.
Add "Duplicate model" button

It creates a copy of the current model, prompting the user for a new
name.
Fix bug where "Save as" was overwriting model

Now, explicitly set the modelId to -1, causing a new model to be
created in DataTransfer#postModel.

I think this will work. It’s late, though, and my brain may not be
fully functioning.