WIP on UF-112: fix onResize() behaviour to work as intended by GWT's LayoutPanel system

Almost done. The general concept that onResize() should only bubble down from the root to the leaves
and that parents are responsible for ensuring that their direct children are laid out within their
bounds (usually by filling the parent completely) has proven correct.

The hurdle that remains is the resize behaviour of UberTabPanel, which is based on the GwtBootstrap
TabPanel, which is not a LayoutPanel. It will need some onResize() behaviour to set the size of the
tab container. This onResize() logic should not attepmt to refer to ancestor nodes in the DOM or
widget tree.