Resolves: fdo#86978 append formula cells to track instead of tree

Cells in FormulaTree are assumed to be tracked already and their
dependents be notified. Also postpone tracking until all listeners are
established.

Change-Id: I7f27fba979fe231e3d3cd071fcc8a273142cb3f3
(cherry picked from commit 573f5dfba805b733dd2da62bde3cd5d9d25879d9)