rowdata to tuple storage format

After certain table changes the storage format of the table changed into row data. Furthermore indexes were stored as row data instead of the default tuple format.

On top of this, three issues appeared with indexes set to tuple format: 
- AbstractIndexStatisticsService had some assumptions on data always being row data (this is not changed)
- TupleStorageDescriptions#getKeyBytes()  returned not the correct key bytes, problematic with mixed order scan
- '>' operator skipped over one row too many 
This should probably be abstract by default.  I don't think any should return `null` though, otherwise they would be lost during ALTER, etc.