Auto-scroll sidebar as the feature window is scrolled

[jkuester]

Currently the active scenario button is updated as the feature is scrolled, but in long features, the scenario button that is active can soon be hidden from view because it is below the bottom of the viewport. We should automatically scroll the sidebar when we cannot see the active scenario button.

[TobiTenno]

.scrollIntoView on the sidebar at the same time we "active" it