Add projected xrefs to genes rather than transcripts by default if there is no equivalent type in the target database.

tables in the production database.

corresponding analysis_description.

Add the following proxy methods:

* get_all_object_xrefs()    alias for get_all_DBEntries()
* get_all_xrefs()           alias for get_all_DBLinks()

These have no documentation as of yet.

changes to get it to do what I think it should do - 1) staging and staging2, 2) add an initial mapping_set entry if this is  new species 3) warn if there is no mapping_set entry but this is not a new species - in this case I the genebuilders should be adding the old one since this is the scenario we want to catch! (need to check the assembly hasn't changed), 4) dry_run, ie preview mode