Update variational inference model to use new generate isoscape function

[VimWizardVersace]

required_geotiffs is no longer a necessary argument. the required geotiffs and their order are instead inferred from the model's save state

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[VimWizardVersace]

looks like you need to switch back to ddf_import_common(). also does this need an integrate into ddf_common first?

Done.

The ddf_common changes have been submitted