Update issue pages for ES support; Article tweaks

* Article: Match attribute name for `attributions`
* ContentBase: Match how we're searching for classes to how we're storing
  them; Account for page numbers that come in as strings
* Tag: Fix search query
* Article Mapping: Tweak some mapping parameters to optimize how we intend
  to search for things
Fix latest_news lookup; Add `exists`/`missing` support to search filters

* ContentBase.search: Both `with` and `without` will now turn `true` or
  `false` values into `exists` or `missing` filters on the given field