DatasetService: add method to wrap RAI to Dataset

It is useful to be able to wrap not just ImgPlus objects, but also any
RandomAccessibleInterval, to a Dataset.

This method will make it easier to display RandomAccessibleInterval
objects with ImageJ, beyond only ImgPlus and Img.
DefaultImageDisplay: refactor image class test

There is now a dedicated method for testing whether a class is
compatible with the image display, for readability.
Dataset: remove redundant interface declaration
DefaultImageDisplay: support display of RAIs

We can now easily display any RandomAccessibleInterval, not just Data
objects, thanks to DatasetService#create(RandomAccessibleInterval).
Merge branch 'wrap-rais'

This branch adds support for displaying RandomAccessibleInterval objects
that are not Data objects, by wrapping them as such automatically.

So now you can say:

ij.ui().show(myRAI);

In particular, this is great for image objects returned by ImageJ OPS,
which are very often RAIs but not ImageJ Datasets.