disable AlphaBlend only if more 10 consecutive error and never success...

 avoid "wrong positive" unsupported AlphaBlend detection.
Add turnpoint radius for first & last tunrpoint in Task Overview dialog.
"Will this be the finish?" question before add Waypoint can't be removed before refactoring usability of task edition.
Fix "Multiselect Picto" drawing for start or finish Line Turnpoint.
Merge branch 'TaskOverview' of https://github.com/brunotl/LK8000