* Add query enhancements opt-in switch to query bar (#17232)
Makes our language updates more visible to users and removes mentions of Kuery as a separate language. Users still get the old lucene experience by default, but have the option to opt-in to "experimental query features" directly in the query bar. Goal is to get more feedback by making these new features more prominent and less of a jump from lucene.
* fix test
This overhaul of the docs structure puts Kibana's documentation more
inline with the structure that is used in Elasticsearch. This will help
us better organize the docs going forward as more docs are added.
This also includes a few necessary content changes for 5.0.
