Added optional protocol method that is called when camera source is loaded

This is a small commit related to issue #86 that I opened and subsequently closed. I added an optional protocol that is called when the camera source is loaded. This allows the developer to set initial camera settings by calling the VCSimpleSession methods after the camera is loaded from the delegate. 
Good idea, but you should check to make sure that the receiver can actually respond to that selector lest we end up with people who have not implemented it getting crashes constantly