Lots of new stuff for ADAM...(TODO: clean up this commit message)

o Using Spark instead of Hadoop
o Dropped GenericRecords in favor of Avro Specific objects
o New count example
o Add referenceId field
o Renamed the flag fields and fixed the way they are set (using default of false for null)
o Exposed flag for dictionary encoding of strings
o New pileup -- lots of work here
o Using Parquet predicate pushdown
o Increase default block size from 50MB to 256MB
Fixup
Fixup