Finished up timeout/reset for editor

> Tested window.onunload - it cannot run alerts but using
addBlock/saveCanvas i confirmed that it does run
> Added global variables for idleTime/Interval to reset them (originally
after you got kicked out you will still get the alert every minute)
> Reset using clearInterval(setinterval object)
> minor fix with imageholder (scales images to window width now, but not
to height)