Drive stepper steps from workflow config

#### Need
The stepper currently renders all three steps it knows about for every workflow. These are

1. Reference Assembly
2. GTF Files
3. Paired-End Sequencing Data

This shows 3 in places where it is not required/desired.

Instead, we need to look at the workflow.yml parameters section, and only display workflow steps that are configured for the stepper (e.g. have a variable with a value we care about)