[WIP] SPARK-2360: CSV import to SchemaRDDs

Implements RFC 4180 for parsing comma separated value files into Schema RDDs, which includes:
* Optional header line
* Handling quoted fields
* Handling new lines inside quoted fields

Adds two new methods to SQLContext
* csvFile: Takes a path and returns a SchemaRDD
* csvRDD: Takes an RDD[String] and returns a SchemaRDD

__TODO:__
* Every field is assumed to be of type String. We can either infer types (using a sample of data) or let user specify types of columns.

Hey Cheng. Thanks for the suggestion and other comments. I looked into this and another CSV tokenizer. Unfortunately, these tokenizers do not support reading from an Iterator. The support/code needed to make them work with an Iterator is no less than doing it from scratch, especially because a CSV row can potentially span multiple lines of the input iterator. 

I applied your other comments.