Checklists now support grouping by placing a group of checklists
under a <group> node.
e.g. /sim/checklists/group/checklist
The group can have a <name>, which is used by the checklist dialog
and can be used by other interfaces, such as the FG1000.
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.
