DVR, CR feedback: change dvrTrait and timeTrait properties on NetStreamLoadTrait into a generic getTrait/setTrait scheme. Update VideoElement finishLoad method accordingly. Remove createDVRTrait and createTimeTrait methods from NetLoader, and add a 'processFinishLoading' stub (@private), and have DVRCastNetLoader override it in order to add the custom DVRTrait and TimeTrait.
