SE - Add toggle AI force group path following

This is for Brad

He would like the ability to define in the SE whether AI groups should stay on their designed courses even when targets of opportunity arise.

Currently surface and submarine groups will tear off after detected threats and never get back to their original course, greatly limiting the careful course plotting the scenario author laid out.

The toggle will be per scenario and exposed somewhere in the SE's UI.

At this time it will be one setting per scenario. Ideal might be a per-group setting as well as per-group type but that is not the intent of this feature request.