Separate catalog login from rest of workflow

[streino]

The current 4-step workflow (with catalog login as step 1) doesn't work well when users want to apply several transformations in a row.

Once they reach step 4 of the workflow, they actually want to go back to step 2 to select another transformation (or filter set) instead of step 1.

It would make more sense to log in once and then iterate on a 3-step workflow.