WIP fix elastic search date mapping and search issues

Elastic search isn't happy with saving blank dates so we put in some
place holder ones and mark them as such when indexing documents. We then
remove the place holders and markers when we pull the dates back out.

This also means that death_date:>$some_date etc works as expected when
using the search.

Still needs some tidying up and testing, especially src/models.js which
is a bit hacked togther