[ADAM-1978] Add additional filter by convenience methods. #1983
I tried to be careful with method names.
Methods that filter out/remove matching records are named
def filterUnalignedReads(): AlignmentRecordRDD
Methods that filter out/remove records that do not match are named
def filterToParent(parentId: String): FeatureRDD def filterToPrimaryAlignments(): AlignmentRecordRDD
Methods that filter on numeric values are named
def filterByScore(minimumScore: Double): FeatureRDD