Update calling convention for pre-integrated IMU measurements in IMUKittiExampleGps, fix scope problem in plot3DTrajectory and make sure that all accessed values are of type Pose3

The calling convention for pre-integrated measurements was outdated. Now it is necessary to create a 'PreintegrationParams' object, and the object holding the summarized measurements is of type PreintegratedImuMeasurements.

Also, the accessors for objects of type Values have been changed. simply using .at is no longer possible, and it is necessary to use, e.g. .atPose3 or .atVector. Changes were made in IMUKitteExampleGPS and plot3DTrajectory to accommodate this new behavior. plot3DTrajectory was further modified to reduce the scope of the main 'for' loop. The scope was too broad (probably as result of a typo modifying the code from GTSAM 3.2.1 to GTSAM 4.0), causing the final pose to be drawn every time, and for the 'hold' state to be inappropriately toggled so that only two states would ever wind up being drawn at the same time.