Add a new sensor propagator (addSensorPropagator)

The Add Sensor Propagator example demonstrates the following:

• How to create a new sensor propagator
• How to register the propagator
• How to calculate the apparent signature
• How to access different feature types in the terrain.

A sensor propagator is responsible for taking in a group of parameters stored in a DtSignaturePropagatorArgs class along with the absolute signature of the object being detected. It returns an apparent signature which represents how well the sensor detected the object. Hence the base class is called DtSignaturePropagator.

This propagator adds an additional check on signature. It takes the apparent signature calculated by the parent class,DtSignaturePropagator, and checks if the target is inside a forest areal feature. If so then the apparent signature is further reduced by half.