Versions of C API tracker functions without timestamp

In TrackerInterfaceC.h, there are versions of osvrDeviceTrackerSendPose, Position, and Orientation that don't require a timestamp but the other functions don't have a non-timestamped version.

One fix would be to enable passing nullptr to mean ("now") the same way the VRPN routines underneath do.  Another would be to make the replicated functions without Timestamped in the name.
