Patch _get_service_values() for groups

Do not try to look up service values when dealing with a group
selection.
Get previewing working against a group

This genericizes the error messaging and refactors some of the inputs to
the router call.
Re-disable save button when previewing a preset

This just does a check against the service dropdown.
Assert _get_service_values() call in preset save

Adds a check to make sure we do not get anything back that looks like a
group (which we should not during this call).