Tweak scenario template designer (instantiate intervention policies)

[YohannParis]

Some scenario template designs require one or more intervention policy.

• Decision making
• Horizon scanning
• Value of information ("Planned inte

However, a model may not have any policy yet and a user is forced to exit the scenario template designer and create the policies first - very annoying.

Issues:

• Rewrite the phrase from "Select intervention policy (historical)" to "Planned intervention policy (optional)"
• When we click "Add more intervention policies", we should have a dropdown + text field combo that allows to type in a name (if I want to instantiate a new, placeholder policy) or search for one in a list.
• Sort the intervention policy and configuration lists in the dropdown in the same order as in the operators (i.e. newest at the top) and consider putting the creation date in smaller font to allow the user to distinguish those with the same names (happens when you create a few scenario templates)
• Fill in some text for the "Description" of the automatically created configurations and intervention policies - for example, This is a configuration created from "Baseline" with (low, high) value for the parameters "beta" and "gamma.