Rename specs in DenseRowTextStorageSpec
Introduce Encoding.isPrimitive
Remove extra and unused indexDictionary in DenseRowTextStorageV1
Filter out struct/list features for pivots
Merge pull request #196 from ambiata/topic/pivot-no-structs

Filter out struct/list features for pivots
Added extra quality notes from todays meeting.
Merge pull request #193 from ambiata/topic/notes

Added extra quality notes from todays meeting.
Remove unused FileSystem import
Change ValueState to handle any ThriftLike value
Extract common setup for priority/namespaced mappers
Changed okCounter var to val
Added type alias MutableFact
Extract PriorityTagDerializer for reducing prioritized thrift values
Pass State function into PriorityTagDeserializer constructor to ensure correct handling