add the youtubeSyncedAt method to the ResourceInterface and implement it in the Channel and Video classes.
add a method to return the channel id.
add prepareUrl method.
add youtubePublishedAt method that will return the published at date.
Merge pull request #3 from Vinelab/improve/synchronizer

Add utility methods that help expose Youtube related data about channels and videos, also improves the way Synchronizer works with given models/resources.