Interface style changes should either happen retroactively, or explain that they don't

[nougatmachine]

When changing from sidebar view to drawer view in the preferences, from the point of view of the user, nothing happens and it apparently isn't working. Of course, what's going on is that changing the interface style doesn't happen retroactively to windows, so the window needs to be closed and re-opened. Ideally, we would have the change take effect instantly. But if this is not possible for some technical reason or another we should still have a notification of some kind explaining that the window needs to be closed and reopened, perhaps as a dialogue box that pops up after the user changes the interface.