[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.

Ok if the standard dictates that only double quotes are allowed, it is actually confusing to allow arbitrary quotes (it is one thing to allow single quotes since they might be common, but I wouldn't allow arbitrary length quotes). This is adding unnecessary complexity to both the interface and the implementation.