Condensed internal data storage of RowRelation

[CodeLionX]

Proposed Changes

• Changed internal data storage from columns: Set[UntypedColumnDef], data: Seq[Map[UntypedColumnDef, Any]] to cols: Vector[UntypedColumnDef], data: Vector[Vector[Any]]
• aligned RowRelation unary operations (like insert, where, ...) to new data store
• THIS MEANS: operations are performed first, before the data is converted to Seq[Record] for putting it into other Relations or returning it

Related

• depends on #98 (pls merge first)

[CodeLionX]

For me, this PR also cleans the internas of RowRelation, so we can do the tests in a new branch.