Clearing data selection does not clear previous saliency result dropdown list

[brianhhu]

I think clearing the data selection input should clear out other parts of the app, e.g. previous saliency map result dropdown. This should be a relatively simple fix to include logic to check for this whenever the data selection is removed. I believe this is already done for model predictions and the saliency maps themselves, without sacrificing the ability to cache previously computed results.

Steps to reproduce:

• Load image in data selection panel
• Compute saliency map
• Remove image in data selection panel
• Dropdown of detections/classes still exists