update order of inserting new split panel

this ensures that the panel is added before the new item is selected so
the any scroll position it applies is preserved.
wip
formalize show/hide methods
update show/hide support

only resize non-hidden children - this removes the need for custom
resizeChildren implementations
fix typo
cleanup docs - remove unneeded resizeChildren implementation
code format
update docs - remove unneeded resizeChildren implementation
update docs
remove relic of mistaken commit
update docs
update the internal current index before calling superclass method
add methods to cancel pending resizes
request children resize when changing the tabbar