'Return a dict of savefig file formats supported by this backend,
where the keys are a file type name, such as \'Joint Photographic
Experts Group\', and the values are a list of filename extensions used
for that filetype, such as [\'jpg\', \'jpeg\'].'

@classmethod
def get_supported_filetypes_grouped(cls):

    groupings = {}
    for (ext, name) in six.iteritems(cls.filetypes):
        groupings.setdefault(name, []).append(ext)
        groupings[name].sort()
    return groupings
