window / tab transitions (for tabview and gide)

[rcoreilly]

need to be able to move content easily between a window and a tab. should be simple as transferring trees but should test that -- the tab view should then provide this functionality of dragging a window in or a tab out to a window. The main question is then whether a new popup item goes straight to a tab or not -- need that api in place..

[rcoreilly]

no issue of popups going into tabs -- gide has clear policy that works well. dragging tabs to windows and vice-versa is lowpri for actual usage -- should do eventually.