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
How about?
```python
from translator import (FORMAT_URIS, FieldcodeCFMapping, StashCFMapping,
                        GRIB1LocalParamCFMapping, GRIB2ParamCFMapping,
                        CFConstrainedGRIB1LocalParamMapping,
                        CFGRIB2ParamMapping, CFGRIB1LocalParamMapping)