Trigger sticky-footer recalculation via events

* `updateSticky` triggers recalculation of sticky footers; it does *not*
  recalculate sticky headers, because that will always require a scroll
  event
* trigger `udpateSticky` on expand/collapse and tree insertion
Merge pull request #1175 from reciprocity/feature/sticky-triggers

Trigger sticky-footer recalculation via events