Move ShimContext to its own file
Move AlterTableHelper into BasicDDLFunctions
Bundle bits of ALTER state into a struct
Pull ColumnName into public class
Allow group index specification to writeRow. Add overload.
Track drop, meta and data changes for group indexes during alter
Consolidate defintion change
merge nathanlws: Cleanup, and fix, group index handling during ALTER

Merge pull request #1020 from nathanlws/sql-layer/streamline-alter-gi-handling
https://github.com/FoundationDB/sql-layer/pull/1020
Update copy constructors to be consistent, even when nothing needs to be copied in that class.
Track a version number for the generated group.
Persist generated storage format descriptors.
Add conversion for data as well as meta-data.
Add format for Protobuf in Persistit.
Add unit test and IT tests.
Update copy constructor.