Pbixray

Added a new property `relationships` to the model which returns a dataframe with schema:

FromTableName | FromColumnName | ToTableName | ToColumnName | IsActive | Cardinality | CrossFilteringBehavior | FromKeyCount | ToKeyCount
-- | -- | -- | -- | -- | -- | -- | -- | --

The `statistics` now surfaces the `StructureModifiedTime` and `ModifiedTime` for a column.

Bug fix affecting column with compressed dictionaries