GA Task: start at departure, remove start-end popups, draw WP lines

For General Aviation: if close to the departure airport consider departure WP already reached and task started, don't display start and finish popups. GA pilots are using the task as their flight plan so first and last WP are the departure and destination airports and they are usually not doing a competition. If we are at departure airport we can consider start line already crossed. And to avoid to display start and and end task popups while beeping during the delicate take off and landing procedures is better for GA.

For GA the intermediate waypoints are usually of type LINE, and doesn't matter where we cross the line (bisector) to switch to the next WP, the field "sector radius" is not used. So here with this change only for GA the intermediate WPs as LINE are drawn always of the same size independently by zoom level. This because in case of more WPs close to each other (for example the WPs defining a circuit pattern) with high level of zoom the lines (if related to a distance on the ground) can cross each other resulting in an ugly and confusing aspect.

LoadGpxTask.cpp is now considering by default intermediate WPs of type LINE only for GA and of type CIRCLE for other categories.