TOG-145 #comment Support different captions sources #time 1d

Add settings for differentiating between captions source:
1. Embedded - set configuration flag “showEmbeddedCaptions” to true.
2. API - default.
3. External - set configuration flag “useExternalClosedCaptions” to
true..
Merge pull request #1154 from kaltura/TOG-145

TOG-145 #comment Support different captions sources #time 1d