[PATCH 24/51] filters: Rewrite the submitter autocompletion code

[Finucane, Stephen]

> We now have a nice(r) autocompletion widget that will popup the list of
> options directly underneath the input fild. A few changes are done in
> this commit that couldn't be split any further:
> 
> - Use jQuery's $.ajax() for the completion query
> - Use the application/json content type on the completion answer to
>   allow jQuery to directly create an object from it instead of giving
>   back a string (because of the text/plain content type)
> - Crafted more logical objects in the json answer ie all properties are
>   at the same level instead of the default queryset serializer that put
>   the object fields in a 'field' sub-object.
> - Use selectize.js for the autocompletion widget logic
> 
> A slight change in behaviour is that we now don't allow "free form"
> submitter search, ie we need a valid completion to search with that
> specific person (through its primary key). I didn't remove the backend
> logic that allows the "free form" mechanism, but maybe we should.
> 
> v2: Squash the unit tests fixes into this patch (Jeremy Kerr)
> 
> Signed-off-by: Damien Lespiau <damien.lespiau at intel.com>

Parts of this are so similar to my change it's scary: we clearly read the same Django docs.

What happens if a submitter doesn't have a name, though? This is possible as 'Person.name' has the 'null' and 'blank' attributes set to 'True'. In my case, I had to use the id as I couldn't be sure the name would be present.