Fix highlight draw to cope with cut layers.

Add efficiency improvement for a highlighted layer to not be drawn twice.
Fix vik_track_get_length_to_trackpoint() so with the first track point it returns zero, not the entire track length!
Really enable C99 mode.
Enable a history of requested positions.

Positions are stored on specific Go To requests (such entered position coordinates or to waypoint/track positions).
Currently panning and zooming do not modify the requested position.
Moving backwards and forwards through the list is supported sort of like a web browsers history of pages.

As the positions are not specifically named (just raw coordinates),
 nothing advanced like showing the list of positions or jumping over multiple positions is offered.

Finer details such as the maximum size of the history list are controlled by Viking's internal preferences.