Resolve "Change PedestrianPositionProcessor to use interpolation of PedestrianFootStepProcessor"

Closes #260 (closed) Closes #262 (closed)

• Simplify tests
• Write text into CHANGELOG
• Write tests for the interpolation method
• overwrite Pedestrian.getPosition() with Pedestrian.getPosition(simTimeSec), which would then use the interpolation method?
• in clearFootSteps() should we keep the last entry (which can be used for interpolation)? --> No, new field currentFootStep, this is because there the whole list is saved & used in "FootStepProcessors" and they would need to make sure to ignore double occurrences
• Look at code where pedestrian.getPosition() would make sense to get exchanged to the interpolated position? E.g. in NelderMead or OverlapProcessor? --> This would be in a new issue/branch then
• Remove the "currentFootStep" field in Pedestrian again and use the "LastFootSteps" provided in VTrajectory (then with a minimum capacity of 1)?
• resolve #263 (closed) first
• How to deal with requested interpolation if a Pedestrian has an outdated FootStep? Check with @hm-kleinmei

if(currentFootStep == null){
	return getPosition();
}else{
	if(time > currentFootStep.getEndTime()){
		// This happens for example if a pedestrian is waiting (see Events)
		// TODO: check with Bene K. if this is okay, or a better way?
		return currentFootStep.getEnd();
	}else{
		return FootStep.interpolateFootStep(currentFootStep, time);
	}
}