The strategy used here for ColorView and ChannelView has been
implemented in a much more general way for ReinterpretArray. It makes
sense to leverage the Base implementation. Plus, now that
`reinterpret` is no longer restricted to `Array`, it turns out that we
run into certain dispatch problems that stem from changing the
dimensionality to handle/subsume color channels. The solution here is
to introduce a `reinterpretc` that is specifically for handling
colors.

This definitely breaks old code.

This should be more performant, and now that we have a generic
`reinterpret` we can cope with the consequences.

The final version of support for reinterpreting arrays with offset
axes requires that the first axis starts with 1. Consequently we now
reshape before we reinterpret. This led to a surprising number of
cascading changes.

Also fixes the Base._length deprecation.