Update design form lists when research is completed

[Monsterovich]

This PR fixes a small issue: when the research completes, but the item doesn't appear in the list until you manually click on any other of the design parts category buttons (body, propulsion, cannons) and then click back, or re-open the design form completely.

[past-due]

Unfortunately this section of the UI still uses the old method of creating / refreshing widgets. That method has several disadvantages, but most importantly: it can break the ability to click buttons if they are “refreshed” (which is actually destroying and re-creating) while attempting to do so.

There were previous efforts to rewrite how other sections are handled - such as the production, research, etc side views - to avoid this “difficulty clicking” issue. I’m reluctant to re-introduce this issue to another section (especially when it fixes a fairly small issue, and also - like those other sections - the “trigger” for refreshing is unpredictable to the user, so it ends up creating the same problem where clicks don’t always have an effect).

Additionally, we probably don’t want the order of the displayed buttons to change while the user is attempting to interact with them, which this could also cause.

Given all of that, I think this is best solved by a future rewrite of these widgets to use the new method (which would include handling of when new items might be added while the user is attempting to interact with them - perhaps not even automatically, but with a button that appears and can be clicked to refresh the list).

[Monsterovich]

@past-due Is it possible to come up with some kind of temporary solution?