Fix backwards compatibility issue with ES results

When ElasticUtils used pyes, pyes would convert datetime-ish
looking strings into Python datetimes. When we switched to
pyelasticsearch, we lost that and datetime-ish things were
coming back as strings like '2013-05-20T15:55:11'.

This fixes that.
allow for statistical facet type
fixed tests for statistical facets
Fix get_mapping examples to have properties