Keep options (collapse all, settings) frozen while scrolling

I'd like the options to be frozen while scrolling. Per my previous bug report, saving uncollapses all panes. If you have scrolled down to a later structure in structure-view, this presents a major workflow inconvenience. You have to scroll all the way up to the top structures just to collapse the panes again. Keeping the options frozen at the top will keep it so that you don't have to scroll to access these settings.

Start by reproducing the issue in the structure-view Atom package: scroll to a later structure, then check whether the options controls remain accessible. Trace the options and scrolling entry points; done means collapse-all and settings stay frozen at the top while scrolling.

Written by the indexing model from the issue text.