Feature: add mean curve to properties

[RemDelaporteMathurin]

Users could want to compare the mean curve for tungsten with the mean curve for copper.

In that case, users would need to be able to add the mean curve to the database.

We could add a button "Add to database" that pops when a mean curve was computed.
This would trigger the "Add property" form where the pre-exponential and activation energy values are already filled in.