Dimensions with linking for ticks and labels

Dimensions can link to either a DataArray or a DataFrame for ticks or labels (depending on Dimension type).

## DataArray links
The link object should hold a series of indices that indicate a single vector to represent the ticks or labels. The dimension which holds the relevant values should be indicated by `-1`.

## DataFrame links
The link object should hold a single index which defines the Column to represent the ticks or labels.

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This replaces AliasRangeDimension, which becomes a RangeDimension that links to the DataArray that holds it, and DataFrameDimension, which becomes a SetDimension (or any dimension now) that links to a DataFrame.

Start by locating the definitions and tests for Dimension, AliasRangeDimension, DataFrameDimension, DataArray links, and DataFrame links. Trace how dimensions currently represent ticks and labels, then verify that the replacement model supports the link contents and dimension changes described in the issue, with tests covering both link types.

Written by the indexing model from the issue text.