* [tribe] Init docs
* [docs] Init es client section
* [docs] Link to client api, move client library docs to core development section
* [docs] Add tribe server settings
* [tribe] Link to elasticsearch tribe docs
* [tribe] Document which nodes server configuration points towards
* [docs] Add index link to elasticsearch clients section
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.