Add config option for using fixed view on preview endpoint.
Add config option for using fixed view on preview endpoint.

The view can be specified by setting the preview.view config option. An
example is shown below:

    preview:
        view:
            columns:[2]

In the above example, all calls to the preview endpoint will use a view
composed of only the concept with ID 2. This is an example taken from
varify to use only the sample column in calls to the preview endpoint.

Signed-off-by: Don Naegely <e690a32c1e2176a2bfface09e204830e1b5491e3@gmail.com>

chop-dbhi/cilantro,chop-dbhi/cilantro,chop-dbhi/cilantro