Four small tweaks, again

* Added position:relative to #passages.
* The Jonah toolbar no longer appears if Undoing is off, and the
"bookmark to here" link no longer appears if bookmarking is off.
* Custom scripts now have access to the interval used by
scrollWindowTo(), in the variable scrollWindowInterval.
* Copy-pasting passages in the story map now alters the pasted passage's
name to be unique.