Metarelate Types

Gen translations is updated to use the newly released Metarelate API.

This reproduces 
iris.fileformats.um_cf_map 
and 
iris.fileformats.grib._grib_cf_map

with one exception: a mistake in um_cf_map caused a line to be written twice, which should not occur; this pull request removes that repeat line
FORMAT_URIS is just the data format rdf:type URIs we support.  We really should be using notation, not the full URI for attributes.

I have replaced this with the notation, the attribute by URI behavior should be deprecated from the metarelate API.  (I will do this as a separate activity)