New MediaPlayer (gb.media)
Create a new 
MediaPlayer.
A MediaPlayer is based on a GStreamer element having the 
"playbin" type.
  - 
Parent: An optional container for the new control.
- 
Type: The type of GStreamer plugin implemented by this MediaControl. It's "playbin"by default.
- 
Polling: The pipeline bus polling period in milliseconds, between 10 and 1,000. It's 250 ms by default.