Set index:'not_analysed' setting on content_type field
Index fields with correct type in ElasticSearch

Previously, everything was converted to a string before indexing in ElasticSearch.
This caused issues where certian filters may not work as expected (such as a greater than filter on an integer field)

This commit changes this by adding type conversion into the ElasticSearch backend.
Exclude filter fields from _all. Explicitly include search fields in _all