Added getWriterByExtension method

Added a method to FormatService to directly get a writer for a given
id, based purely on suffix matching.

This allows bypassing of the Checker logic, which may not be applicable
when an Image source is not available for opening - because it has not
been written yet.

Only returns non-DefaultWriter instances.
Relaxed OMETIFF translation

Removed the exact match flag when searching for a translator for
creating OMEMetadata and TIFFMetadata when translating to OMETIFF
format.

This was only working in tests because it was testing through the legacy
layer which always translated using a MetadataStore wrapped in
OMEMetadata.