Fixed <<back>> in specific situations

* <<back>> now works better when Undo is off in Sugarcane. Previously it
would mess up the variable state in cases when link variables were in
use.
* <<back>> and <<return>> now work when restoring a Jonah state via
bookmark.
* <<back>> also now works when clicked in a past passage - previously it
would act as if it was in the present passage.
* Fixed the IDE's monospace font using the normal font's size instead of
its own.