clone-with-props now properly clones Om components

I modified the nav examples to show what this gets us. Now I can "mutate" children to set the active? property of the selected tab, for example, without the user having to do her own check of all keys while laying out the tab.

Also, the `:on-select` handlers on top level nav elements now get called if set, along with the current nav-item `:on-select` handlers.