Feat/video  Add Video storage and retrieval endpoints 

To Test:
 - Using Postman GET
 http://s1pitchperfect.azurewebsites.net/api/videos/url/53e4115151265a6cc67bf9a0
 - Should return secure url to video on Azure
 - Copy that URL into FireFox browser
 - Watch the video

Details:
/videos POST
Create Video document in Mongo
Return video _id

/videos/url/:video_id  GET
Return secure access URL to video on Azure