Convert Discover to New Platform

[timroes]

Conversion of "Discover" to the new platform. The discover base folder can be found in src/legacy/core_plugins/kibana/public/discover. The app contains out of the following components:

• Discover App (./top_nav, ./controllers)
• Saved Search Embeddable (./embeddable)
• Doc Table (./doc_table) - the actual main discover table
• Field Chooser (./components/field_chooser) - the field chooser on the left side

Not directly sitting in Discover, but considered to be part of the Discover app are also:

• Context View (<kibana_core_plugin>/public/context) - view documents in their context
• Single document viewer (<kibana_core_plugin>/public/doc_viewer)

The following tasks are still outstanding:

• Move plugin out of the Kibana plugin
• Move plugin to new platform
• Move UI to React (EUIfication)
  • Discover App
  • Doc Table (see [DISCUSS] Datagrid component specifications eui#1689)
  • Field Chooser
  • Context View
  • Single document viewer
• Complete Angular removal (all of the above components are still mainly using Angular)

[elasticmachine]

Pinging @elastic/kibana-app

[timroes]

Closing this in favor of "Deangularization" row in https://github.com/elastic/kibana/projects/44