revamp slider_iframe for timeouts

JS in slider_iframe.html was fraught.  Assignment via DOM not as bullet-proof
as the brain-dead document.write().  In fact, this is the only way it works.
see slider_iframe.html SHA of same date for diff.

* deprecate postMessage complexity
* delete unneeded ancilliary js assets
* new function Dbg(m,o) for debugging message + object
* more cleanup of vars via jshint