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