SCIFIOImgPlus: Update Metadata use

In the latest ImgLib, net.imglib2.meta.Metadata was renamed to
ImgPlusMetadata.

The use in SCIFIOImgPlus now reflects this change.
Removed SCIFIO tutorials

Per https://github.com/scifio/scifio/issues/10, the tutorials component was
falling terribly out of date, was not released with the main SCIFIO project,
and had dependencies that did not make sense for the SCIFIO core (e.g. OMEXML).

Thus it has been split out to its own project. See
https://github.com/scifio/scifio-tutorials