Expose functions for reuse and promote types.
Add Waypoint List dialog.

The enables viewing lots them with their basic properties (name, date, altitude + comment).
Being in a simple (treeview) list, each column is sortable.

Implementation is very similar to the Track List dialog.
Use Waypoint list dialog in TrackWaypoint layer menus.
Use Waypoint list dialog from Aggregate Layer menus.
Merge branch 'WaypointsList'
[DOC] Update help with text and images for multi-layer TrackWaypoint lists and statistics dialogs.