Add support for push down filters in parquet sources

This includes bumping parquet to version 1.6.0rc2
As there is only one class with this we could also do:
public constructor (fields: Fields, paths: String*)
private constructor (fields: Fields, paths: Array[String], filterPredicate: Option[FilterPredicate])
and add a 
def withFilter(filter: FilterPredicate) = new FixedPathParquetTuple(fields, paths, filter)
From the user the syntax looks like:
```new FixedPathParquetTuple(fields, "a", "b").withFilter(myFilter)```