Change tracking cue: InsetText and InsetCollapsible

Change tracking cue: InsetText and InsetCollapsible

* Underline or strike through the label as if it was text (it is).

* Strike through deleted InsetText, but let RowPainter handle the case of
  non-MultiPar text insets.

* Change the colour of the frame as a cue, unless its colour is customised (not
  Color_foreground). (Essentially do the border of CharStyles like Tabular does
  it already.)

* The change info needs to be reset when entering InsetText. Otherwise labels
  are painted with the change of their n+1-th parent.