OMEROFormat: parse OMERO credentials when writing

The Parser component is not called (nor should it be) when a Writer is
initialized. Instead, the Writer itself should take care of extracting
the OMERO credentials from the destination string.

This process could almost certainly benefit from some further thinking,
but it works for now.
Bump to scifio 0.6.1 release

This fixes an ImgSaver bug when writing non-interleaved planes.
OMEROSession: fix method order
OMEROSession: throw FormatException for errors

Even though it is oh-so-convenient, returning null buries problems.
In this case we can throw FormatException since upstream public callers
all throw it already anyway. So let's do proper error reporting.
OMEROSession: obtain core info from ImageMetadata

The Writer infrastructure takes care of populating the ImageMetadata
appropriately before asking for planes to be written. However, there is
of course no way it could possibly populate the format-specific metadata
fields. So we need to extract the dimensional extents, pixel type, etc.,
from the populated ImageMetadata rather than the uninitialized
OMEROFormat.Metadata-specific fields.