Structured streaming support for consuming from Kafka

This is the parent JIRA to track all the work for the building a Kafka source for Structured Streaming. Here is the design doc for an initial version of the Kafka Source.
https://docs.google.com/document/d/19t2rWe51x7tq2e5AOfrsM9qb8_m7BRuv9fel9i0PqR8/edit?usp=sharing

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Structured streaming doesn't have support for kafka yet. I personally feel like time based indexing would make for a much better interface, but it's been pushed back to kafka 0.10.1

https://cwiki.apache.org/confluence/display/KAFKA/KIP-33+-+Add+a+time+based+log+index