The change introduced in commit 8c7fc119 to go to the last checklist
on open causes a problem when the first checklist has multiple pages.
If the last opened checklist did not have multiple pages, the previous
and next page buttons are still shown.
This commit runs the same binding as used by the combo box to reset
the visibility of these buttons immediately before the page is
displayed.
These are then attached to buttons on the checklist dialog allowing
the user to ask the computer to execute the checklist step, which
they can observe.
Checklists may now be split into individual sections made up
of <pages> containing the <item> tags. Each page is displayed
individually with Previous/Next buttons to allow navigation.
Checklists items also support <marker> tags. These display
a marker when a ? button is pressed next to the checklist item.
The format is identical to that of the tutorial system.
Checklist items now support a <condition> element that evaluates
when the checklist item is complete, and is used to provide color
coding in the checklist dialog.
