SES-2015 : Deprecate static methods in RDFFormat that have dynamic
equivalents in Rio

Users do not realise that the static methods in RDFFormat do not work
with third-party implementations, where the dynamic methods in Rio do,
due to the use of java.util.ServiceLoader to discover and instantiate
the RDFFormat constants.
SES-2015 : Provide backwards compatibility with RDFFormat.register

This is not meant to be a fix that enables both systems to work together
in the long term, as it is not ideal to be tracking a static list in
RDFFormat.
Merged in SES-2015 (pull request #244)

Deprecate RDFFormat.forFileName and RDFFormat.forMIMEType