MAINT:Change ontology term identifier to bigserial

The term identifier in the ontology terms table was set as a big int, thus
adding new user-defined terms was cumbersome, with this change in place those
the term is now a bigserial.

I have also changed the ontology file in the beast, so people WILL HAVE to
reload their databases.
Yes, I am going to change it so it defaults to NULL. Thanks for catching
this.

On (Nov-07-14|10:07), Antonio Gonzalez wrote:
> >  	ontology_id          bigint  NOT NULL,
> > +	old_term_id          bigint  ,
> 
> should this be not null? 
> 
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> https://github.com/biocore/qiita/pull/581/files#r20026151