To show the current bandwidth to user and for debugging purposes current bandwidth is required to be reported. This pull request adds the bandwidth estimate in the progress event.
Also the bandwidth details are added in the audio track in load event. There is another pull request which reports the video track information
1. Loaded event will give the information about available video tracks
2. selectedVideoTrack prop will give the interface to select the video track. This prop will take the height of the video (Similar to youtube like 144p, 350p etc) and set the video track. If height is 0 then all video tracks will be added to list so that it will work like 'Auto' in youtube
* added listener for timedMetadata event.
* added callback in RCTVideo for the timed metadata
* exposing onTimedMetadata to JS
* added forgotten method declaration
* returning array of string values
* added metadata type to the array
* added onMetadata method
* overridden onMetadata method on exoplayer2
* added format of return value from onMetadata
* added function reference in README file
