We don't want wrapping labels to cause tooltips to
have excessive height, so we need to set a reasonable
value for width-chars, without forcing short tooltips
into a full line length. Also be careful to respect
preexisting line breaks (we have such examples in
widget factory).
The position child property is problematic, since it
requires us to emit notification for all children when
inserting a child early in the list of children.
Remove the property from all ui files.
It's not a hugely complicated file, but it's easier to deal with some of
the details of tooltip windows styling if we have a UI file to edit,
instead of source code.
