Adding ADAMSequenceRecord schema to adam.avdl
Added SequenceDictionary class

Including test suite.
Extended Bam2Adam to create a SequenceDictionary .dict Parquet file
Adding the ListDict command.

Includes
(1) a new Projection-like class, for the fields from the ADAMSequenceRecord schema.
(2) A new enumeration, ADAMSequenceRecordField, to be used within that class.
(3) ListDict command itself, which simply prints the order, name, and length of the sequences in teh sequence dictionary.

Removed sortByKey in ListDict -- this was causing an error with sorting Option[ReferencePosition],
need to ask Matt about this later.
Adding two example BAMS, that differ only in their @SQ sequence dictionary entries.
Adding the CompareAdam command