For linking later.

- Replace alias range dimension test with self-link test.
- Test RangeDimension -> DataArray link

Deprecation warning

  FutureWarning: Using a non-tuple sequence for multidimensional
  indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`.
  In the future this will be interpreted as an array index,
  `arr[np.array(seq)]`, which will result either in an error or a
  different result.

For both Range and Set dimensions

Using group redirect method is unnecessary for SampledDimensions since
they don't support linking

Return unit directly for DataArray links.
Return unit of indexed column for DataFrame links.

Return label directly for DataArray links.
Return name of indexed column for DataFrame links.

- Removed DataFrameDimension class.
- Removed all mentions of alias range dimension from DataArray.
- Removed associated tests and test sections.

Should not be negative either.

Should not have negative values except one -1.

Can now write through to the linked data object when setting label and
unit on RangeDimension:
- RangeDimension ticks cannot be changed.
- RangeDimension label linked to DataArray changes the DataArray label.
- RangeDimension label linked to DataFrame raises error: The column name
  of a DataFrame can't be changed since it's the name of a field of
  a compound data type, which we can't change.
- RangeDimension unit linked to DataArray changes the DataArray unit.
- RangeDimension unit linked to DataFrame changes the DataFrame column
  unit.
- SetDimension labels cannot be changed.

pylint warning codes
  W0611: Unused import
  W0612: Unused variable