Add method BBMOD_Animation.add_event_time(_seconds, _name)

[kraifpatrik]

Currently we have add_event(_frame, _name), but the number of frames in Blender can differ from the number of frames after conversion to BBANIM, based on used FPS settings - which makes the method hard to work with. We should add a method that takes the animation time in seconds. That could be easier to work with.