Allow bfconvert file patterns to use configurable number of digits

[mlinkert]

See ​http://lists.openmicroscopy.org.uk/pipermail/ome-users/2014-December/004921.html.

Each of the replaceable number fields should allow a user-specified number of digits, so that e.g.

bfconvert input.ome.tiff output_%ssss.tiff

writes files name output_0000.tiff, output_0001.tiff, ...

Using "%s4" or similar instead would also be an option.

[jamoore]

Splitting due to milestone decoupling.

[mlinkert]

No ongoing work here; this is primarily a string parsing and formatting issue, as bfconvert itself shouldn't need to be changed. The two methods to update would be ​https://github.com/openmicroscopy/bioformats/blob/develop/components/formats-api/src/loci/formats/FormatTools.java#L1011 and ​https://github.com/openmicroscopy/bioformats/blob/develop/components/formats-api/src/loci/formats/FormatTools.java#L1021. This may end up being breaking, so if not possible for 5.2.0 it's likely best to push to 5.3.0.

%[width][field type] similar to ​http://docs.oracle.com/javase/6/docs/api/java/util/Formatter.html is probably nicer to work with than "%ssss" or "%s4" or similar, but feel free to use whatever seems easiest to parse. The main thing is being able to specify the 0- (for numeric) or whitespace- (for string) padded width for any currently-supported field in the filename, and maintain backwards compatibility with existing behavior as much as possible. "docs/sphinx/users/comlinetools/conversion.txt" will also need to be updated with the new width syntax.

[sbesson]

See also ​https://github.com/openmicroscopy/bioformats/issues/2490