18.4: Added recent descriptions button
when adding new waypoint. Backup waypoints before deleting
waypoints and/or tracklogs as well as when exiting the app. Cancel
GPS updates properly when closing app.
18.2: Added auto backup of waypoints and
tracklogs when exit button pressed (Cycles three backup files. This
is for emergency use if data lost). Show grid ref using last known
position. Swapped altitude and acccuracy on main page for
consistency with other versions of app.