Embrace the flexible box model in the widgets

I think that may be overkill.  Instead I added comments above the lines where I use Deprecated, telling us that they should be remove in IPy 4.0.  It's not the end of the world if we forget to remove them, the feature still remains "deprecated", which just means we *may* remove it in the future, not necessarily that we *will* (although I think in this case it's clear that we *will* remove them).