mplay32: Additional improvements for CORE-7910

The patch does the following:

• The MCI device is left open until the user closes the file, opens a new file or quiets the application.
  If the user opens a video, the video window now shouldn't disapear anymore when playback is stoped.
• The video window isn't reset to the device's default one when playback stops and one can toggle
  between a singe window or two windows regardless if the media is playing or stoped.
• Since the device stays open all the time now, bIsOpened isn't needed anymore. Instead the device
  handle itself can be used to see if a file is opened. Also bIsPaused isn't needed anymore, since the
  device status (playing, paused, stoped) can be queried from the device itself.
• in OpenMciDevice(), increase szNewTitle to MAX_PATH * 2 (MAX_PATH for the filename, 256 for the
  title and another 3 for the chars inbetween them).
• merge ResumePlayback() and PausePlayback().
• Wipe out the file extension to device mapping. Since MCI can do this for us, it isn't realy needed.