Three separate patches here:

1. Create Create tables for RNAProduct. Basically renamed copies of
Translation tables "translation" and "translation_attrib" plus a
new column rnaproduct_type_id, complete with a corresponding table
rnaproduct_type, which is used to distinguish between RNA-product
types;

2. Add type RNAProduct to object_xref.ensembl_object_type. This is
needed to support e.g. miRBase xrefs for microRNAs;

3. Add type rnaproduct to stable_id_event.type. This is needed to
support mature RNA products in stable-id mapping.