Define uncertainties for very steep slopes

[astehno]

Uncertainty is being applied for EurOtop Eq 5.18 as a random sample. We need to:

1. perform the uncertainty routine to define a value for this equation's combined uncertainty with wave/WL uncertainties (Abbie)
2. sort out how that value should be applied as a CL when there may be a combination of OT from very steep and regular slopes in the final storm suite (group)