Revert delay of WWidget::load()
Issue #4888 called for the delay of
WWidget::load() until after rendering.
A common use case for
load() is to lazily create and add a widget to the widget tree, like
DeferredWidget in the widget gallery.
Some of those widgets may use
The original motivation for issue #4888 was that a child may be added to the parent in their constructor before the child is sufficiently initialized. This is no longer possible in Wt 4, so that reason is no longer valid.