[SPARK-1981] Add AWS Kinesis streaming support

right, i knew you would ask about this!  

scala can't differentiate between the two overloaded methods with default arguments in this situation:  https://groups.google.com/forum/#!msg/scala-user/FyQK3-cqfaY/fXLHr8QsW_0J

it's totes weird, i know.

i'll remove storageLevel to simplify.  i'd like to keep initialPositionInStream in case there's a need to differentiate.