Improve UX for adding DecayTreeTuples
During Dillon's (great!) presentation yesterday, I noticed people not knowing where to click after they selected stripping lines and bookkeeping paths.
This is not a perfect solution but should at least help people understand that they need to add a DecayTreeTuple before they can submit their request. It adds a visual indicator that signifies that the user must add a DecayTreeTuple for each selected decay before they can submit their request.