Removed the rawData member from wbImage_t
Minor corrections to timing routines in class CudaTimer and wbTime_stop()

* To be consistent with the Linux / OS X / Coursera timing routines, Windows now reports elapsed time in seconds (previously time was reported in milliseconds)
* Fixed a compilation error due to undefined symbols NSEC_PER_SEC and MSEC_PER_SEC if compiling with POSIX timers on Linux