Add getContainingPage().

Controls can call this to get an object reference to the page that
contains the control, if any.
Fix to layout() dLabel when the caption changes.

This has been bugging me for years and I finally did something
about it. When you change the caption of a dLabel, it isn't
enough to refresh() it, you need to call layout() on its Parent,
which I've been doing manually in my code and tending to forget
until I encounter it the next time.

Fixed to automatically call that parent.layout() when dLabel's
Caption changes.
Fix remaining self.super() calls in ReportDesigner.
Remove trailing whitespace.
Fix segfaults in editable columns.

I was getting segmentation faults in Linux. Turning off the updating
of the selected cell when it is editable resolved the issue with no
observed negative effects.