Enable editing of all added curves at once

[mollybsmith-noaa]

I thought we had an issue for this already, but I couldn't find it, so here's a new one:

We've had a request to let users edit all their added curves at once, for example changing all statistics to "Bias". This came up in 2019 but it involves a particularly obnoxious portion of the client-side code, so I was happy to let it die in the absence of additional requests. However, it might tide people over until we have the chance to introduce batch plotting, so it's time to get it done!

[github-actions]

This issue is stale because it has been open 90 days with no activity.