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.
Fixed NPE in FormatTools.getFilename

The ome.scifio FormatTools was mistakenly querying axes instead of
channels. Fixed this to look through channelDimTypes.

Note that this is not perfectly analogous to the legacy behavior because
of lacking a MetadataRetrieve with individual channel labels. Presumably
if an OMEMetadata was translated to the target Metadata though, the
  channel names would be preserved.
Fixed NPE in OMEXMLMetadataService

Was calling getValue() on the channelSamplesPerPixel. If that field
wasn't populated, a NPE would be thrown.

Now check for null before calling getValue().