plan visualization: set the height in proporation to the width

Previously, we would calculate and the height in absolute pixels based
on figure size and dpi, without taking into account the zoom level of
the plan.

Fix #196. Note that the description there is slightly erroneous, it was
more that height was being dramatically over-set for wide plans.
editor: also resize divs containing plans when emptying them

Addresses another part of #196.
Merge branch 'ui-js-fixes' into production
raco: update with groupby fixes