ImgSaver: fix javadoc

Why use /* */ when you can use /** */ and get proper javadoc?
ImgOpener: attach metadata to ImgPlus objects

ImgPlus now provides a table of properties accessible via the
getProperties() method, so let's attach the affiliated Metadata
and ImageMetadata objects there, for potential later use.
ImgSaver: attach metadata to ImgPlus object

Similar to 896d41ce8eebbc1b966cd09dcc8044dbbf402cbb, let's attach
the writer's metadata object to the ImgPlus being written.
Merge branch 'attach-metadata'

This branch makes the format-specific Metadata accessible from the
resultant ImgPlus(es) after reading the image(s) using ImgOpener, or
writing the image(s) using ImgSaver.

I have some vague concerns about memory issues when doing this, but
haven't found anything concrete to substantiate them yet. We can always
back out this change if it proves to be a problem. But having access to
the format-specific metadata will be very useful for ImageJ-OMERO, whose
OMEROService needs to report back the ID of a newly uploaded Image
object, even if it was scifio-omero that took care of the upload itself.