Click on end of interval marker seeks to start of marker

[protyposis]

A click onto the end of an interval marker (where the mouse pointer snaps) results in a seek to the start of the marker. It should seek exactly to the snapped position at the end.

Also clicks between the snapping areas at the start and end of an interval should result in seeks to the clicked positions.

While at it, it would also be helpful if the marker snapping could be deactivated via the config (SeekBarConfig.snapToMarkers: boolean = true (true by default).