BlankAudioSource (#64)

* Added MutedAudioDataSource class

Provides a silent audio track of the a specific duration.
This class can be used to concatenate a DataSources that has a video
track only with another that has both video and audio track.

* Enable MutedAudioDataSource in Builder

Using addDataSource(dataSource) adds a muted audio track when necessary.
This can be skipped by calling addDataSource(AUDIO, dataSource) and
addDataSource(VIDEO, dataSource).

* Fix the usage of the MutedAudioDataSource in the TranscoderOptions builder

* Makes the buildAudioDataSources function clearer

* Restart timed-out checks

* Updated muted audio mediaFormat values

applied PR suggestions

* small PR changes and fixes

* Renamed class to BlankAudioDataSource

and removed unncessary check in canReadTrack()

Co-authored-by: cbernier2 <48560005+cbernier2@users.noreply.github.com>