SCIFIOFormatWriter delegates canDoStacks

SCIFIOFormatWriter now delegates all canDoStacks calls to its paired
ome.scifio Writer, instead of forcing each loci.formats delegating
writer to perform this delegation.

Updated APNGWriter to remove unnecessary method overrides.
Updated OMEXMLMetadataService Metadata population

Instead of trying to preserve old ImageMetadata, when populating an
ome.scifio.Metadata using OMEXMLMetadataService, clean ImageMetadata
will be generated.
Converted OMEXMLFormat

The loci.formats OMEXMLWriter and OMEXMLReader have been converted to a
single OMEXMLFormat as SCIFIO components.

All necessary supporting classes were converted as well.

The loci.formats reader/writer were converted to delegators for the new
Format.