Added subtitle model and API

Thoughts on this approach? 

Tests forthcoming...
@BenjiLee @ormsbee 
I asked @yro (Greg Martin) He says:
		
"i don't know the answer to this, this is a lyla question... we only GENERATE one transcript/language, but that can be edited and stuff."

I forwarded this question to @Lyla-Fischer and will get back to you.