Implement "Speed" option on RTSP "PLAY" command by Changing Live555 Code
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Architecture:
* Live555 RTSP stack is used by the client component of UTC's Prism surveillance product.
* In particular, the streaming driver (session_lnvr.dll) of Prism client uses this open source software.
* The driver statically links the Live555 library.
* The driver communicates with the Live555 RTSP stack via RTSPAsyncAdapter, which is based
      on testRTSPClient demo application of Live555 but significantly modified to fit UTC architecture.

* Changes to Live555 code are limited to liveMedia/include/MediaSession.hh and liveMedia/RTSPClient.cpp

Change Details:
1. RTSPClient.cpp:
   * Implement new method, static char* createSpeedString(float speed)
   * Enhance setRequestFields() method

2. MediaSession.hh:
   * Implement get() and set() methods to access 'speed' property in MediaSession and MediaSubsession classes.

3. All changes in (both) Live555 moduled are guarded by __UTC_PRISM__ macro.